Validation: use default language if not provided

[System-Glitch]

Proposal

When using validation manually, not providing the Language field in the validation.Options will trigger a panic: runtime error: invalid memory address or nil pointer dereference.

We should load the built-in default language (en-US) if the option is omitted. Or we could use an empty language that would return only the name of the entry.

Possible drawbacks

Loading the default language for every validation can reduce performance a bit. This would still be very much recommended to use the option. This would need to be properly documented.

[BowlOfSoup]

As you suggested in the discusion on Discord, we could also detect if a language is been given. If not, we just return the entry name/input-as-is without translation, thus not using a language lookup in validator.go:processAddedErrors().