Internationalization is the process of developing the codebase so that it can easily be translated into other languages. Internationalization is often abbreviated as i18n (because there are 18 letters between the i and the n).
Topics for this handbook page:
Singular/plural forms; explain, that singular isn’t always used for 1 item
Translator comments for placeholders, requirement
Explain difference between context and translator comments
Languages have varying word orders, and complex grammatical and syntactic rules. “Lego” messages, put together from lots of pieces of text, possibly with some indirection, are very hard or impossible to translate.
It is better to make every message a complete sentence, each with a full stop at the end. Several sentences can usually be combined much more easily be into a text block, if needed.