If you work within its capabilities, remembering that it cannot be used to highlight changes in topic text, Project Synch will work very reliably. However, you may still encounter some problems in certain situations, particularly if you don't follow the instructions.
Since project synch automatically modifies your translated version of the project you should always create backups before synchronizing. This is simply good security policy, and it is particularly important if you are synchronizing existing translations that were not created with the help of project synch (see below). Then you can always resort to the backup if anything goes wrong.
Structural changes made in the translated version will be deleted!
Please always remember that this function is only for updating translated versions to reflect changes made in the original project. It is assumed that the translator does not make any structural changes to the project. If the translator makes structural changes like adding new topics, moving or deleting topics etc. these changes will be deleted when you synchronize the translated project with the master!
Again: The translator is not allowed to make any structural changes to the project or to alter anything in the project configuration settings or (except translation of the keywords). Translating the content is fine, but structural changes made by the translator will probably be deleted during synchronization and may also cause problems!
Can you compare an existing translation with the original master project?
You can do this even if the language pair was not created with the Project Synch tool, provided that the structure and Topic IDs of the two project versions match precisely. If this is the case you can use the Compare by Topic ID option to turn the two projects into real siblings that can be synchronized normally.
For full details see Synching existing projects.