Trailing dots in localization files

The localization files have trailing dots but they are not consistent. For example, the messages in `src/rules.js` file all have dots at the end, but the messages in `en-US.js` do not.
Everyone seeing this issue, please provide some feedback on this to decide in which direction to go:
- with trailing dots.
- without trailing dots

Start by comparing the message definitions in src/rules.js with the localization messages in en-US.js, focusing on trailing punctuation. The issue is not ready for implementation until the project decides whether messages should consistently include or omit trailing dots; done would mean that decision is documented and the localization files follow it.

Written by the indexing model from the issue text.