Some games include a language.txt marker in the unpacked local tree, similar
in spirit to account_name.txt. Installs and updates now carry the launcher
language alongside the account name so those game-provided marker files are
rewritten before staged files are promoted into local/.
The Tauri command boundary keeps the UI setting vocabulary as de/en, then maps
it to the file vocabulary expected by games: german or english. Unknown values
continue through the existing DEFAULT_LANGUAGE path, so the marker file falls
back to english just like script launch arguments fall back to en.
The transaction layer deliberately reuses the same first-match traversal helper
for both marker files. The searches stay independent, so games may place
account_name.txt and language.txt in different directories if their archive
layout requires that.
Test Plan:
- just fmt
- just test
- just frontend-test
- just clippy
- deno task build
- git diff --check
Refs: none
ddidderr
9bafd981d7
