Implement default_variables in i18n.translate

[sveneberth]

I want to translate this tooltip:

scope_code = StringBone(
    params={
        "category": "2 – Scope",
        "visibleIf": 'code_type == "universal"',
        "pattern": rf'^[{"".join(CODE_CHARS)}]+$',
        "tooltip": i18n.translate(
            "viur.shop.allowed_characters",
            defaultText="allowed characters: {{chars}}",
        )(chars=CODE_CHARS),
    },
)

I know the variable chars before the translation string should be resolved with the request language. But at this point I cannot provide the variables.

We should extend i18n.translate's __init__() with a default_variables parameter and later merged this together with kwargs in translate()

[sveneberth]

Solved already in a subclass for the shop: https://github.com/viur-framework/viur-shop/blob/fabe13057ccd9b802c32aa781f68d20e5cef0b6e/src/viur/shop/types/__init__.py#L57-L71