Locale uninstall tests fail

The locale uninstall tests are currently failing.

This is because LocaleUninstallFunctionalTest::testUninstallProcess():

• Enabled a new language using locale_add_language()
• Calls DrupalWebTestCase::drupalCreateUser() that calls user_save() that calls the Field API to store the fields
• The field API fails in field_multilingual_valid_language() because the newly enabled language is not yet reflected in the static cache of language_list()

This was passing before because the static cache of language_list() was never primed before calling user_save(). It is now primed somewhere during the initial cron run.