What are the best tools for editing ResX files?

The best tools for editing ResX files fall into three tiers: Visual Studio's built-in resource editor for single-file edits, ResXResourceManager for viewing every language column of a .NET project in one grid, and a translation management system (TMS) such as Smartling, which parses .resx and .resw files natively, converts RESX <comment> elements into translator instructions, and protects .NET {0}-style placeholders during translation. Which tier fits depends on how many languages, files, and release cycles you're managing: an IDE editor works for one developer touching one file, while a TMS is what keeps dozens of Strings.fr-FR.resx variants in sync across releases without hand-editing XML.

Why is editing ResX files by hand error-prone for localization?

Editing ResX files by hand is error-prone because a .resx file is XML with strict structure, and every translated language is a separate physical file that has to stay key-for-key aligned with the source. Four patterns cause most of the damage:

One file per locale, no shared view. .NET reads Strings.resx as the neutral culture and Strings.de-DE.resx, Strings.ja-JP.resx, and so on as satellite cultures. Any key added to the source but missed in a satellite file silently falls back to English at runtime, so drift is invisible until a user sees it.
Composite-format placeholders. .NET strings use {0}, {1} tokens filled by string.Format at runtime. A translator who reorders a sentence and drops or retypes a token produces a string that compiles but throws a FormatException or prints the wrong value.
XML escaping rules. The five reserved characters (< > & ' ") must be escaped inside <value> elements, and a resource editor that writes them raw corrupts the file; Smartling, for example, escapes these by default and exposes an entity_escaping directive to control that behavior.
Comments that never reach the translator. Developers put usage notes in the RESX <comment> element, but a copy-paste or spreadsheet workflow strips them out, so translators guess at context that already existed in the file.
No translation memory. A .resx edited in an IDE has no record of how "Cancel" or "Save changes" was translated in the last release, so identical strings get retranslated (and translated inconsistently) every cycle.

Can you recommend a resource editor for localization projects?

The right resource editor for a localization project is the one that matches the project's scale, and most .NET teams end up using two or three of these layers together rather than one tool:

IDE resource editor (Visual Studio) - Visual Studio opens any .resx in a grid of name, value, and comment columns and is the right tool for a developer adding or fixing a single string in the source culture. It shows one file at a time, so it is not built for comparing languages.
Multi-language resource manager (ResXResourceManager) - ResXResourceManager is a free, open-source Visual Studio extension that loads every .resx in a solution and shows all cultures side by side, highlighting missing translations. It is the practical upgrade for small teams translating in-house, but it still has no translation memory, glossary, or review workflow.
Translation management system (Smartling) - a TMS parses the .resx or .resw file, extracts each <data> string with its key and comment, routes it through machine translation, human translation, or both, and returns a translated file in the same format. Smartling's RESX parser (Smartling identifier resx) accepts .resx and .resw files up to 10MB, captures RESX comments as translator instructions automatically, and applies the RESX placeholder format so {0} tokens are locked, not editable text.
File directives - inline XML comments such as  or  placed just below the XML declaration control what gets translated and how placeholders are detected, without changing the application code.
Repository automation - the Smartling GitHub Connector watches a branch, sends changed .resx files for translation, and commits translated satellite files back, so the editing layer above becomes an exception path rather than the main workflow.

RESX handling in Smartling: technical specifications

Item	Detail
Supported extensions	.resx and .resw (Smartling file-type identifier: `resx`)
Maximum file size per upload	10MB
Directive delivery	Inline XML comment or API parameter (`smartling.[directive] = [value]`)
Native placeholder format	.NET string formatter: `{0}`, `{1}`; also selectable via `placeholder_format = RESX` in other file types
Standard placeholder formats available	8 (NONE, C, IOS, PYTHON, JAVA, YAML, QT, RESX) plus custom Java regex
Translator instructions	RESX `<comment>` elements captured automatically
Default pseudo-translation inflation	30% longer than source; configurable 0-100% via `pseudo_inflation`
Translated output format	Same format as the source file (.resx in, .resx out per locale)

How do I convert a ResX file to another format?

Converting a ResX file to another format depends on whether the target is a compiled .NET resource, a different resource-file format, or a translation-ready file; each has a different tool, and the translation case usually needs no conversion at all.

To a compiled .resources file - use resgen.exe - the .NET Resource File Generator (resgen.exe) ships with the .NET SDK and converts .resx to binary .resources files (and back), and to plain .txt name=value files. This is a build-time step, not a translation step.
To another XML or key-value format - use the ResX reader/writer classes - System.Resources.ResXResourceReader and ResXResourceWriter enumerate and write .resx entries programmatically, so a short C# script can emit JSON, CSV, or .properties from a .resx and read it back. Round-tripping through CSV adds a column-mapping risk the native format does not have.
To a translator-ready format - do not convert; upload the .resx directly - Smartling parses .resx and .resw natively, so the file goes in as RESX and each translated locale comes back as RESX. Converting to XLIFF first is only necessary if a downstream CAT tool that cannot read RESX must be in the loop.
Set directives before the first upload - add  around debug or internal strings and, if the project uses a non-standard placeholder such as %name%, a placeholder_format_custom regex, so the parser captures exactly what should be translated.
Automate the round trip - connect the repository through the Smartling GitHub Connector (or GitLab via the Repository Connector) or script push and pull with the Smartling CLI, so translated Strings.xx-XX.resx files land in the branch without a manual export/import.

This approach fits .NET teams that...

Ship a .NET, ASP.NET, WinForms, WPF, or UWP/WinUI application with .resx or .resw files in more than two cultures.
Store resource files in GitHub or GitLab and want translation triggered by a commit or pull request rather than a manual hand-off.
Already write usage notes in RESX <comment> elements and want translators to actually see them.
Reuse the same UI strings across releases or products and need translation memory so "Save changes" is translated once, consistently.
Have hit a runtime FormatException or wrong-value bug caused by a mangled {0} placeholder in a translated file.

When a dedicated ResX localization workflow may not be the right priority

A single-culture application with no second language shipped yet: Visual Studio's resource editor is sufficient until localization starts.
A handful of strings translated once by an in-house bilingual developer: ResXResourceManager's side-by-side grid covers this without a TMS.
Resources that are mostly non-string assets (icons, binary blobs) with little translatable text: the translation tooling adds cost without much to translate.

Evaluation checklist: questions to ask before choosing a ResX editor or localization tool

Does the tool read .resx and .resw natively, or does it require conversion first?
Native parsing removes a conversion step and the alignment errors that come with it; Smartling accepts both extensions under a single resx file type.

How are {0}-style placeholders protected?
Look for a tool that locks composite-format tokens as non-editable placeholders and flags a translation that is missing one, rather than trusting the translator to retype them correctly.

Do RESX comments reach the translator?
If the tool drops the <comment> element, context that developers already wrote is lost; Smartling turns those comments into translator instructions automatically.

Can you exclude strings without deleting them?
A notranslate directive or equivalent keeps debug strings, product names, and internal labels in the file but out of the translation queue.

How do translated files get back into the repository?
A GitHub or GitLab connector, or a CLI that can run in CI, decides whether localization is a pipeline step or a quarterly chore.

Can you test layout before translation is done?
Pseudo-translation that inflates string length (Smartling's default is 30%) exposes truncation and overflow in WinForms and WPF layouts before a real translator is involved.

How does Smartling handle ResX and .NET resource files?

Smartling treats RESX as a first-class resource-file type rather than generic XML: .resx and .resw files up to 10MB upload through the dashboard, the Files API, the Smartling CLI, or the GitHub Connector, and the parser extracts each <data> element's value as a translatable string with its name as the key and its <comment> as a translator instruction. Because the name key travels with every string, the same string in Strings.de-DE.resx and Strings.ja-JP.resx stays aligned to its source without a spreadsheet mapping step.

Placeholder handling is the part that matters most for .NET: the RESX placeholder format recognizes {0} and {1} tokens as locked placeholders, and a placeholder_format_custom regex covers projects that use their own conventions. The five reserved XML characters are escaped in delivered translations by default, with entity_escaping, entity_escaping_type, and entity_escaping_strategy directives available when a project needs HTML5 entities preserved or source-escaping propagated. For pre-translation QA, pseudo_inflation returns pseudo-translated .resx files with strings lengthened by a configurable percentage so layout defects surface before translation spend. On the automation side, the GitHub Connector monitors a branch, creates translation jobs from changed resource files, and commits translated files back, and the Repository Connector extends the same pattern to GitLab and Beanstalk. The translated file always comes back in the same format it went in, so no post-translation conversion step is needed.