[Enhancement]: Use translation strings for validation messages

[TIIUNDER]

Describe the solution you'd like

The current validation error messages are some combined strings of "Please enter a valid" and the field name, for example "Please enter a valid firstname". This works for English, but not for other languages. For example in German we get "Bitte geben Sie eine gültige vorname" ein. First of all, "Vorname" needs to be capitalized, second it's "Bitte geben Sie einen gültigen Vornamen ein". So grammar, is also important.

It should use translation strings from the po/mo files of WooCommerce for every single field.

Describe alternatives you've considered

No response

Additional context

No response

[TIIUNDER]

Same problem for "+ Add appartment, suite etc."

[TIIUNDER]

And also for select dropdowns like "canton", We need "Wähle ein Kanton" and not "kanton". Also in some cases it might be "eine" or "einen" etc.