After configuring groups they must be processed. This means that definition texts are indexed and needed caches are populated. For this, you need to run processMessageChanges.php to process the changes. You can run this maintenance script as given below.
From the Translation extension directory:
The above mentioned script finds out changes in the messages and makes only these changes available for processing to save time. The changes include:
- changes in English message contents
- changes in message documentation contents
- mismatching contents for group/language
- additional entries in a file for a group/language (i.e. externally maintained)
For new style groups head to Special:ManageMessageGroups and rebuild (import) all languages. On this special page file based message groups can be managed (FileBasedMessageGroup). This page allows updating of the file cache, import and fuzzy for source language messages, as well as import/update of messages in other languages.
Note: For old style groups use sync-group.php. This script also works for new style message groups, but you still need to use Special:ManageMessageGroups to build the caches.
For new style message groups you can use Special:ManageMessageGroups to handle fuzzying. For old style message groups you need to track the changes manually and use fuzzy.php to mark translations as in need of an update.
See also 
- translatewiki:Repository management and related pages have some information of general use