Allow translateOrDefault to user app locale

[rhwilr]

Currently the translateOrDefault method requires a local parameter.
This PR adds a default value of null to the locale parameter.

This way the locale defaults to the current app.locale. It also adds consistency with the translate method.

[Gummibeer]

Hey,
Looks good! Could you add this feature also to translateOrNew() ? To have this consistency over all translate...() methods.

[rhwilr]

Done.
I also had to make a change to getTranslationOrNew for this to work.

[Gummibeer]

Thanks - good job! I will keep it open for next release. 😊