[FIX] base: allow calling install_lang in RPC

This method is used in Transifex synchronisation scripts and needs to
be called in RPC.
It was the case before 727ef9e0a2ca9308

closes odoo/odoo#110087

X-original-commit: 3b7e4535d358e554f7b089828efb82bc6b0a40e3
Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>

odoo/addons/base/wizard/base_import_language.py

@@ -46,3 +46,4 @@ class BaseLanguageImport(models.TransientModel):
                   ' (Valid formats are .csv, .po, .pot)\n\nTechnical Details:\n%s') % \
                 (self.filename, tools.ustr(e))
             )
+        return True