One possible strategy would be having a default language in code, and supply translations separately.
No matter which localized languages i would have finally, i'd prefer to choose English as the default/fallback language of the documentation.
Code structure provides indexing for your translation database, for example:
Type, NameWithNamespace, OptionalParameterName
"member", "MyProject.Core.Loader.FillSize", ...
You could have a tool that would allow for translation in a UI for each namespace/member.
You can have a separate team of translators looking through the items that have no translation yet, and supply translations.
And you can start shiping a translated documentation as your ship a release as soon as you get the amount of translated items above a threshold.
A changed default translation would indicate that you need a new translation for all other languages too.
Of course, if you do a major namespace-only changes, you can remap the namespaces as an ad-hoc remapping operation in database.
If you run opensource project, it makes sence to use a collaborative online translation tool.
One example of such collaborative translation strategy implemented in production is
https://translations.atlassian.com/
Basically you could just step in and start contributing translations online.
It is set up to translate the products themselves, not the documentation, but the same practice apply.