Why can't my translation ID end with a '.'?

BabelEdit uses the period (.) as a separator to split translation IDs and display them as a tree, as explained here. Therefore, having a '.' at the end of an ID is not allowed.

If you're not using periods in IDs to represent a namespace hierarchy, you can change the format in Configuration → Format to "JSON with plaintext keys, flat view". This lets you use IDs like "Name of the project." with a period at the end.