Clarify `get_translated_string` string argument (#13948)

Co-authored-by: sfan5 <sfan5@live.de>
Co-authored-by: Muhammad Rifqi Priyo Susanto <muhammadrifqipriyosusanto@gmail.com>
Co-authored-by: rubenwardy <rw@rubenwardy.com>

doc/lua_api.md

@@ -4111,9 +4111,10 @@ On some specific cases, server translation could be useful. For example, filter
 a list on labels and send results to client. A method is supplied to achieve
 that:
 
-`minetest.get_translated_string(lang_code, string)`: Translates `string` using
-translations for `lang_code` language. It gives the same result as if the string
-was translated by the client.
+`minetest.get_translated_string(lang_code, string)`: resolves translations in
+the given string just like the client would, using the translation files for
+`lang_code`. For this to have any effect, the string needs to contain translation
+markup, e.g. `minetest.get_translated_string("fr", S("Hello"))`.
 
 The `lang_code` to use for a given player can be retrieved from
 the table returned by `minetest.get_player_information(name)`.