NppTranslatePanel

NppTranslatePanel is a Notepad++ plugin that continuously translates the active document and displays the result in a dockable panel. It is written in C# and targets .NET Framework 4.8.

The plugin supports DeepL API and the free MyMemory Translation API. DeepL requires the user's own API key; MyMemory does not require one.

Privacy policy · Code signing policy · Third-party notices · Releases

Features

• Live translation of the active Notepad++ document
• Dockable, read-only translation panel
• Optional automatic refresh after typing stops
• One-click Translate command and toolbar button that use the selection when present, otherwise the complete document
• Translate Entire Document to override an active selection and always translate the complete document
• Open the current translation in a new Notepad++ tab while retaining the source syntax mode
• Save the current translation as a UTF-8 file with the source extension and target-language filename
• Configurable source and target languages
• Paragraph-level cache to avoid translating unchanged text again
• Manual clearing of the in-memory translation cache from Settings > Application Behavior
• Cancellation of obsolete requests when the document changes
• Automatic splitting of long paragraphs to respect API request limits
• Translation status with provider, character count, API requests, cache hits, and elapsed time
• Privacy-safe local diagnostics that never log document text or API keys
• Optional use of the current Notepad++ editor colors
• Optional matching of the active document's syntax highlighting and editor layout, including Markdown formatting
• Support for both 32-bit and 64-bit Notepad++

Requirements

• Windows
• Notepad++
• .NET Framework 4.8
• Internet access to api.mymemory.translated.net, api-free.deepl.com, or api.deepl.com, depending on the selected provider

The plugin build must match the architecture of Notepad++: use x64 for 64-bit Notepad++ and x86 for 32-bit Notepad++.

Installation

1. Create a directory named NppTranslatePanel inside the Notepad++ plugins directory.
2. Copy NppTranslatePanel.dll into that directory.
3. Restart Notepad++.
4. Open the panel using Plugins > NppTranslatePanel > Show Translate Panel.

A typical 64-bit installation looks like this:

C:\Program Files\Notepad++\plugins\NppTranslatePanel\NppTranslatePanel.dll

Usage

To translate, first use the Translate button on the Notepad++ toolbar. It translates the active selection when text is selected; otherwise it translates the complete document and opens the panel when needed. Alternatively, use Plugins > NppTranslatePanel > Translate. With the privacy-safe defaults, opening Show Translate Panel alone does not send document text anywhere; automatic translation can be enabled explicitly in Settings.

The plugin menu also contains:

• Show Translate Panel — shows or hides the dockable panel.
• Translate — translates the active selection when present; otherwise it translates the complete document. The toolbar button runs this same command.
• Translate Entire Document — opens the panel if necessary and translates the complete active document, even when text is selected.
• Open Translation in New Tab — opens the displayed translation as an editable Notepad++ document and applies the source document's language mode.
• Save Translation As... — saves the displayed result without another API request. The suggested filename retains the source extension and includes the target language.
• Settings — opens the plugin settings dialog.

Plugin commands are available in Settings > Shortcut Mapper > Plugin commands, where users can assign their preferred keyboard shortcuts without imposing global defaults. Assign a shortcut to Translate to use the same selection-or-document behavior from the keyboard.

Automatic translation after editing or switching tabs is disabled by default and can be enabled in Settings. Translation always stops while the panel is hidden so that API quota is not consumed unnecessarily.

Use Settings > Application Behavior > Clear Translation Cache to discard translations cached during the current Notepad++ session. Clearing is immediate and does not start a translation; the next request will translate the affected text again through the selected service.

Settings

Setting	Default	Description
source_language	en	Language code of the source document.
target_language	cs	Language code of the translated output.
debounce_ms	1000	Delay in milliseconds after the last edit before translation starts. Values below 200 ms are treated as 200 ms.
mymemory_contact_email	empty	Optional email sent to MyMemory to increase the free quota.
translator_provider	MyMemory	Selected translation service: MyMemory or DeepL.
deepl_api_key	empty	DeepL API key, encrypted locally with Windows DPAPI for the current user.
deepl_use_free_api	true	Uses the DeepL API Free endpoint; disable for a DeepL API Pro key.
auto_translate_on_edit	false	Starts translation automatically after typing stops when explicitly enabled.
translate_on_tab_change	false	Translates immediately after switching document tabs when explicitly enabled.
synchronize_scrolling	true	Synchronizes vertical scrolling proportionally between the editor and translation panel.
match_source_syntax_highlighting	true	Uses the active language definition and mirrors its syntax colors, font styles, zoom, tabs, indentation, and wrapping.
privacy_notice_accepted_provider	empty	Records the provider for which the one-time privacy confirmation was accepted.
use_npp_styling	true	Uses Notepad++ editor colors for the plugin UI.

Language values are MyMemory language codes such as en, cs, de, or fr. Availability depends on the language pairs supported by MyMemory.

Settings are stored in the Notepad++ plugin configuration area under NppTranslatePanel.

Translation services and privacy

See the full privacy policy for the data sent to each provider, local storage, diagnostics, and user controls.

MyMemory documents a free anonymous quota of 5,000 characters per day. Supplying an email address through mymemory_contact_email raises the documented free quota to 50,000 characters per day.

MyMemory's terms state that submitted segments may be stored on a long-term basis. DeepL processes requests according to the terms of the user's API plan. Do not use either provider for confidential, sensitive, regulated, or third-party content unless sending it to that provider is acceptable and authorized.

Text requested for translation is sent over HTTPS to the selected third-party service. Before the first request to a provider, the plugin asks for confirmation and remembers the accepted provider. Changing providers requires confirmation again. A permanent warning is also displayed in the Translator settings tab.

Declining the confirmation cancels the request, sends no document text, and disables automatic translation.

Selection-only results do not participate in synchronized scrolling because they represent only part of the source document.

The Translate panel also provides Open in New Tab and Save As... buttons. Saved translations use UTF-8 without a byte-order mark. Choosing the original source path requires an additional overwrite confirmation.

The plugin splits the document into paragraphs and caches completed translations for the current session. Only changed or previously untranslated paragraphs normally require another API request. Paragraphs longer than 450 characters are divided into smaller requests.

Code signing

Planned signing provider: Free code signing provided by SignPath.io, certificate by SignPath Foundation.

The SignPath Foundation application is being prepared. Until approval and activation of the automated signing workflow, release artifacts are unsigned. The repository's code signing policy defines the build provenance, approval, signing, verification, and release requirements.

Building from source

Open NppTranslatePanel.sln in Visual Studio 2022 and build one of these configurations:

• Release | x64 for 64-bit Notepad++
• Release | x86 for 32-bit Notepad++

The project restores UnmanagedExports.Repack.Upgrade through NuGet and produces a .NET Framework 4.8 plugin DLL.

By default, the post-build target copies the output directly to the matching Notepad++ installation:

%ProgramFiles%\Notepad++\plugins\NppTranslatePanel
%ProgramFiles(x86)%\Notepad++\plugins\NppTranslatePanel

Writing there may require an elevated Visual Studio instance. To build without writing into the Notepad++ installation, override the destination with an MSBuild property, for example:

msbuild .\NppTranslatePanel\NppTranslatePanel.csproj /p:Configuration=Release /p:Platform=x64 /p:NppPluginsDir64=C:\stage

The resulting DLL is located in:

NppTranslatePanel\bin\Release-x64\NppTranslatePanel.dll

For a 32-bit release, the output directory is NppTranslatePanel\bin\Release.

Architecture

The main components are:

• Main.cs — plugin initialization, menu commands, notifications, and panel lifecycle
• Translation/ChangeWatcher.cs — change debounce, request cancellation, segmentation, and orchestration
• Translation/MyMemoryTranslator.cs — MyMemory HTTP client and response parsing
• Translation/TranslationCache.cs — bounded in-memory paragraph cache
• Translation/Segmenter.cs — paragraph splitting
• Forms/TranslatePanel.cs — dockable Scintilla translation output
• Utils/ContainerSyntaxHighlighter.cs — safe syntax highlighting from Notepad++ language definitions
• Utils/MarkdownSyntaxHighlighter.cs — Markdown-aware highlighting that uses Notepad++ UDL styles
• Utils/ScintillaStyleSynchronizer.cs — active style and editor-layout mirroring
• Utils/PrivacyConsent.cs — provider-specific privacy confirmation state
• Utils/Settings.cs — user-configurable settings
• Utils/DiagnosticsLogger.cs — privacy-safe translation performance and error log
• PluginInfrastructure/ — Notepad++ and Scintilla interop inherited from NppCSharpPluginPack

Current limitations

• Translation requires an internet connection.
• Formatting and the exact number of blank lines are not preserved in the translated preview.
• Syntax highlighting is visual only; machine translation may still change programming-language tokens.
• The preview remains read-only; translated copies are created only through Open Translation in New Tab or Save Translation As....
• The translation cache exists only for the current Notepad++ session and is cleared when translation settings change.

Diagnostics and tests

Translation diagnostics are written to NppTranslatePanel.log in the plugin configuration directory. Each entry contains only the timestamp, provider, character and paragraph counts, API request count, cache hits, duration, outcome, and sanitized error text. Document contents and API keys are never logged.

Build and run the dependency-free core test suite with Visual Studio MSBuild:

msbuild .\NppTranslatePanel.Tests\NppTranslatePanel.Tests.csproj /t:Restore,Build /p:Platform=x64 /p:RuntimeIdentifier=win-x64
.\NppTranslatePanel.Tests\bin\x64\Debug\net48\win-x64\NppTranslatePanel.Tests.exe

License

Licensed under the Apache License 2.0.

The Notepad++ C# plugin infrastructure is derived from NppCSharpPluginPack and the archived NotepadPlusPlusPluginPack.Net. See third-party notices for attribution and dependency licensing.