fix(i18n): support both string and object forms of i18n.sourceLocale

[eintim]

The original implementation assumed sourceLocale was always a string. However, Angular allows it to be either(see schema):

• A simple string (e.g., "en-US")
• An object with properties like code, subPath, and baseHref

When an object was used, the resulting output path included [object Object], causing incorrect output paths or build failures.

This fix ensures compatibility with the full range of valid sourceLocale definitions

[CappuccinoDiAigner]

Thank you for the fix @eintim! This is also a problem for us. Would be great if this could be reviewed. :)