Translating strings are done with the `_t()` function found in matrix-react-sdk/lib/languageHandler.js. It is recommended to call this function wherever you introduce a string constant which should be translated. However, translating can not be performed until after the translation system has been initialized. Thus, sometimes translation must be performed at a different location in the source code than where the string is introduced. This breaks some tooling and makes it difficult to find translatable strings. Therefore, there is the alternative `_td()` function which is used to mark strings for translation, without actually performing the translation (which must still be performed separately, and after the translation system has been initialized).
1. Check if the import ``import { _t } from 'matrix-react-sdk/lib/languageHandler';`` is present. If not add it to the other import statements. Also import `_td` if needed.
1. Add ``_t()`` to your string. (Don't forget curly braces when you assign an expression to JSX attributes in the render method). If the string is introduced at a point before the translation system has not yet been initialized, use `_td()` instead, and call `_t()` at the appropriate time.
1. Run `npm run i18n` to update ``src/i18n/strings/en_EN.json`` (if it fails because it can't find the script, your dev environment predates the script, so reinstall/link react-sdk with `npm link ../matrix-react-sdk`). If it segfaults, you may be on Node 6, so try a newer version of node.
1. If you added a string with a plural, you can add other English plural variants to ``src/i18n/strings/en_EN.json`` (remeber to edit the one in the same project as the source file containing your new translation).
1. Extend your ``_t()`` call. Instead of ``_t(STRING)`` use ``_t(STRING, {})``
2. Decide how to name it. Please think about if the person who has to translate it can understand what it does.
3. Add it to the array in ``_t`` for example ``_t(STRING, {variable: this.variable})``
4. Add the variable inside the string. The syntax for variables is ``%(variable)s``. Please note the s at the end. The name of the variable has to match the previous used name.
- Do not use `_t()` inside ``getDefaultProps``: the translations aren't loaded when `getDefaultProps` is called, leading to missing translations. Use `_td()` to indicate that `_t()` will be called on the string later.
- If using translated strings as constants, translated strings can't be in constants loaded at class-load time since the translations won't be loaded. Mark the strings using `_td()` instead and perform the actual translation later.
- If a string is presented in the UI with punctuation like a full stop, include this in the translation strings, since punctuation varies between languages too.
- Avoid "translation in parts", i.e. concatenating translated strings or using translated strings in variable substitutions. Context is important for translations, and translating partial strings this way is simply not always possible.
- Concatenating strings often also introduces an implicit assumption about word order (e.g. that the subject of the sentence comes first), which is incorrect for many languages.
