I also hard code my UI on lwuit, and i have a variable parentForm on every class so i can easily show previous form. For language change i know there is Localization in the resource editor that you can make use of. Below is how you can access it. I guess the trick is how to set the content of the L10N in the res file in code? On the other hand you can create your own helper classes that mirror the methods below.
Resources theme = Resources.open("/theme.res");
theme.getL10N(id, locale);
theme.getL10NResourceNames();
theme.isL10N(name);
theme.listL10NLocales(id)