Google Maps help: Directions language.

You can select the language in which the driving/walking directions will be given:

Directions in english.

Google map directions in english.

Directions in dutch.

Google map directions in dutch.

If you want to change the distance units (for example: km instead of miles) you must change the generated code.

Locate code:
opts.locale = "<languageCode>";

And add/change the country code:
opts.locale = "<languageCode>_<countryCode>";

For example:
opts.locale = "en_US";

More information about countries with their corresponding language codes.