feat: add option to add default locale

[jreppnow]

No description provided.

[tronicboy1]

I like this! You may be right that add_resource_overriding might do it but I think its much better to have a convenience behavior like this. If you were to add a German l10n, it would be cool to have it automatically go to the English version.

Maybe it might be a good idea to log something to tracing debug if the FTL key was missing from the target locale? That might make it easier to debug.

[jreppnow]

@tronicboy1 I think it would be more flexible to change this line into add_resource_overriding (should be backwards-compatible, as this was a hard error before, although it does change behavior):

axum_l10n/src/fluent.rs

Line 91 in f179928

bundle.add_resource(ftl).map_err(|err| {

Reason: By doing this, you can have multiple back-ups, instead of just one.

[tronicboy1]

@jreppnow
That's a very good idea too! I don't see an issue with allowing the override behavior.

Yes it is a behavior change but not a breaking change so I think it's fair game. You're more than welcome to make another PR for that change!

[jreppnow]

As discussed, superseded by #2.