Add translator's information.

CONTRIBUTING.adoc

@@ -7,6 +7,7 @@
 :contact-fediverse: https://likeable.space/users/tastytea
 :uri-git-format-patch: https://git-scm.com/docs/git-format-patch
 :uri-git-send-email: https://git-scm.com/docs/git-send-email
+:uri-poedit: https://poedit.net/
 
 == How to contribute
 
@@ -35,3 +36,38 @@ link:{uri-branch-main}/AUTHORS[AUTHORS]. Unless you don't want to.
 
 You can also send me your patches via mailto:{contact-email}[E-Mail], ideally
 using link:{uri-git-send-email}[git send-email].
+
+=== Translations
+
+==== Creating a new translation
+
+To create a new translation, copy `translations/{project}.pot` to
+`translations/[LANGUAGE ABBREVIATION].po`, (replace [LANGUAGE ABBREVIATION] with
+the correct abbreviation for your language, e.g. “es” if you are translating
+into Spanish or “pt_BR” if you are translating into Brazilian Portuguese).
+
+Open your new po file with your favourite text editor, (or you may prefer to use
+a translation catalog editor like link:{uri-poedit}[Poedit]), and first edit the
+header section of your file. You will need to replace the text in UPPERCASE with
+the correct values. The easiest way to work out how to do this is to compare it
+to another po file that already exists.
+
+==== Updating your translation
+
+When it is time to update your translation, first update your Git working
+directory. Then do the following:
+
+[source,shell]
+--------------------------------------------------------------------------------
+cd build
+cmake --build .
+cd ../translations
+msgmerge --update es.po epubgrep.pot
+--------------------------------------------------------------------------------
+
+Then open your file and locate the strings that need updating. These will have
+an empty *msgstr* or will be marked “fuzzy”.
+
+_The translation guide is based on
+<https://www.claws-mail.org/faq/index.php/Translator\'s_Information>, licensed
+under GFDL-1.2-only._