Translate selection values computed with methods
Currently only the selection values computed with a list are translated [1], but as seen #2356 (closed) there are some cases which is interesting to restrict the values depending on other fields.
In order to retrieve all the possible translations we should call the method with and empty record (if instance method) in order to retrieve all the possible translations.
[1] http://hg.tryton.org/trytond/file/287383ca412e/trytond/ir/translation.py#l269
[2]