I see you have support for ICU Message Format. What does the UI look like for a complex ICU string? A big issue I come across is that translators aren't typically technical enough to understand the syntax.
I've dreamed of a TMS that understands an incoming ICU Message Format and spits out a non-technical UI for translators to use. Then after translation it merges it all back together into a single ICU Message string.
It's then up to you too either do that on the server, on the client, or at build time. All three are easily possible. If you'd start with a static file then the decoupling and automation tasks will be much more difficult to achieve.
Or: https://tolgee.io/docs/web/using_with_react/react_preparing_...