Define a convention for i18n of Python applications

[benoit74]

• What is the conventional library for i18n of our Python applicatins?
• Is it possible / desirable to have the same solution (or at least a share core) for Vue.JS codebases? (TbD as well, see Define a convention for i18n of Vue.JS applications #28)
• What is the conventional way of using the library? (default settings, file names and locations, ...)

Requirements:

• TranslateWiki must be able to process this format (very light requirement given the fact that TranslateWiki is capable to process almost any file format)
• Right To Left, Pluralization, Placeholders, ... (quite obvious as well)

[benoit74]

First implementation / PoC might be done with openzim/gutenberg#56

TbC because while it is a very important project where i18n is needed, it is also the one with the most custom existing codebase around i18n (almost no library has been used AFAIK, everything is custom-made so effort to integrate with TranslateWiki / adopt a conventional library has to assessed)