This depends on interpolated expression sequences to be ergonomic to use and in most cases, a function that uses this should take it as tstring name...; a typesafe variadic (this is also why it is a class rather than a struct - D only supports this particular feature on classes).

You can use null as a tstring. You can also construct it with UFCS: i"foo".tstring.

The actual translation engine should be set on the application level.

It is possible to get all translatable string templates compiled into the application at runtime.