And then create a standard/base language file (e.g. English -> "en.lua", as it's best known worldwide and easy to translate from) to provide the strings that need to be translated.
Also provide 1 example file of another language, e.g. de.lua, containing the entries with English text
SafeAddString(YOUR_ADDON_NAME_GLOBALLY_UNIQUE_STRING_ID, "Your translation for the other language", 2)
Users can just translate the lines then to their language and send you the files again.
Either share the files via GitHub if your addons are at GitHub, or provide a zip file so one can download, translate and send you the translated lua files again.
You are also able to attach files to your post here.