Thanks for working on this! Overall it looks good. I like the languageCodesEquivalent solution, it's simple and should cover the majority if not all cases we would see.

Rather than showing an additional warning message, what if we only show the "All languages are correct" notice if we determine there is a mismatch between training and drafting source languages? We could change the required languagesVerified message to "I understand, proceed drafting with selected languages".

Reviewed 9 of 9 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @RaymondLuong3)

src/SIL.XForge.Scripture/ClientApp/src/app/translate/draft-generation/confirm-sources/confirm-sources.component.ts line 88 at r1 (raw file):

  private sourceLanguagesAreCompatible(source: TranslateSource, other: TranslateSource): boolean {
    if (source.writingSystem.tag === other.writingSystem.tag) return true;
    return this.i18nService.languageCodesEquivalent(source.writingSystem.tag, other.writingSystem.tag);

nit I wonder if this should take a source[] that we loop through and compare source[0] to each item? Doing this now should prevent us from having to update if/when we go to more than 1 alternate source.

Code quote:

  private sourceLanguagesAreCompatible(source: TranslateSource, other: TranslateSource): boolean {
    if (source.writingSystem.tag === other.writingSystem.tag) return true;
    return this.i18nService.languageCodesEquivalent(source.writingSystem.tag, other.writingSystem.tag);

Regarding the "language confirmation" notice, the existing direction is to have the notice showing all the time with the hopes that the user checks and confirms the languages every time, as a safeguard. @Nateowami may have more to say on this.

Reviewed all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @RaymondLuong3)

src/SIL.XForge.Scripture/ClientApp/src/app/translate/draft-generation/confirm-sources/confirm-sources.component.html line 55 at r1 (raw file):

  @if (showSourceLanguagesNotCompatibleError) {
    <app-notice type="error">
      <span>{{ t("sources_must_be_same_language") }}</span>

If there are multiple training sources and their languages differ, we show a message on the main drafting page and prevent them from even getting to the first step. I believe we should follow this pattern, unless there's a good reason not to.

I think this PR changes that requirement. We've confirmed with the Serval/EITL teams that if we verify the language codes are equivalent then draft quality will not be degraded.

I guess the question on keeping it as a safeguard for all instances would be if we believe selected sources have a high probability of having an incorrect language code set that needs reviewed before proceeding? Otherwise, I'd suggest that only displaying it when we detect a different language code alerts the user draft quality would be reduced but still allow them the option to proceed.

Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @josephmyers and @RaymondLuong3)

src/SIL.XForge.Scripture/ClientApp/src/app/translate/draft-generation/confirm-sources/confirm-sources.component.html line 55 at r1 (raw file):

This is a good point. I would consider multiple training sources with different language codes a hard stop as I don't believe Serval can handle it. I could go either way on the changes in the PR being a hard or soft stop. Serval will handle training and drafting sources being different language codes (but draft quality will be poor).

Ok, cool. It sounds like you have more recent information than I do. Carry on!

Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @kylebuss and @RaymondLuong3)

src/SIL.XForge.Scripture/ClientApp/src/app/translate/draft-generation/confirm-sources/confirm-sources.component.html line 55 at r1 (raw file):

Right. As the PR is currently, it is a hard stop, but it's hard stopping too late in the process. If we're going to hard stop, we need to hard stop at the "landing" page, where the other hard stops are.

Yes, this makes sense. Can you update the JIRA task (title, description, acceptance tests, etc.), as well as updating this PR, to match this new direction?

Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @kylebuss and @RaymondLuong3)

I am getting an error when starting a new draft.

Reviewable status: 3 of 12 files reviewed, 2 unresolved discussions (waiting on @RaymondLuong3)