Add translation instructions for translators

INTERNATIONALIZATION.md

@@ -0,0 +1,35 @@
+# Making Plume available in your language
+
+*You will need to have basic git and GitHub knownledge to follow this guide. But we plan to setup a more user-friendly translation tool in the future.*
+
+To translate Plume in your language, you'll first need to make sure it is listed in the `po/LINGUAS` file. If it is not, you can ask anybody with a development environment to add it (or do it yourself if you have a development environment). Once it will be here, Plume must be launched once to generate all the needed files.
+
+Then you can start translating. Find the file corresponding to your locale, which is `po/YOUR_LOCALE.po`, and open it. Inside, you have a list of strings to translate. There are two kind of translatable strings.
+
+## Simple strings
+
+They look like this:
+
+```po
+msgid "Hello, world"
+msgstr ""
+```
+
+What is next to `msgid` is the string in English. To translate it, just fill the `msgstr` field with the translation.
+
+## Strings with plural forms
+
+Sometimes, strings may change depending on a number (for instance, a post counter). In the `.po` files, these strings look like this:
+
+```
+msgid "One post"
+msgid_plural "{{ count }} posts"
+msgstr[0] ""
+msgstr[1] ""
+```
+
+Then you should fill the two `msgstr` field, one with the singular form, the second with the plural one. If your language as more than two forms, you can add another one by following the same pattern (`msgstr[n] ""`).
+
+## Interpolation
+
+Strings you translate may contain data from Plume (a username for instance). To tell Plume where to put these data, surround their identifier by `{{` and `}}`. The identifier is also present in this form in the English string to translate (this what you can see above, with the `{{ count }} posts` message).

README.md

@@ -9,3 +9,5 @@ It is not yet ready for production use, but we have all the basic features (acco
 Feel free to join our Matrix room: `#plume:disroot.org` to discuss about the project!
 
 If you are interested in coding, check out the [development guide](https://github.com/Plume-org/Plume/blob/master/DEVELOPMENT.md). You can also help by reporting issues, suggesting features, or writing documentation for instance.
+
+If you would like to help by translating Plume, we also have [a guide for you](https://github.com/Plume-org/Plume/blob/master/INTERNATIONALIZATION.md)!