The same thing happens to me, I tried with 3 versions 2.9, 2.10 and 2.11 and I get the same error.

All that's missing is the expression to be able to convert a string to language and be able to use it as in the following example:

set {_l} to "spanish" parsed as lenguage
translate {_msg} to {_l}

It's an excellent addon, the delay is minimal and requires no configuration. It's perfect! ❤️