locale: fix incomplete fallback bundles

[BAMF0]

Fix an error where only the common strings would be used when falling back to embedded locales. This lead to an issue where the raw Fluent message keys were returned rather than actual error messages, such as wc-error-failed-to-print-result instead of "failed to print result".

Additionally, preserve partial resources instead of discarding everything when not all messages could be parsed.

Fixes #11854

[github-actions]

GNU testsuite comparison:

Note: The gnu test tests/cut/bounded-memory is now being skipped but was previously passing.
Note: The gnu test tests/rm/many-dir-entries-vs-OOM is now being skipped but was previously passing.
Skip an intermittent issue tests/pr/bounded-memory (was skipped on 'main', now failing)

[codspeed-hq]

Merging this PR will not alter performance

✅ 309 untouched benchmarks
⏩ 46 skipped benchmarks¹

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_{Comparing BAMF0:main (320fc59) with main (6130076)²}

Footnotes

1. 46 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on main (50ca60a) during the generation of this report, so 6130076 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[BAMF0]

Hmm the French tests seem to be failing unfortunately. They pass on my machine, I will have a look as to why.

[BAMF0]

Ah nevermind, the failing utility (hostid) does not have a french translation available under src/uu/hostid/locales, only en-US.ftl.