Exactly! You’ll have to register the mo file with WordPress in order to provide automatic translation facility on your website. For this, you can use PoEdit, one of the most used cross-platform get-text catalogs.
The first step is to understand the formats:
1. .mo is short for Machine Object. This is used by WordPress in the form of a complied export of your .po files.
2. .po is short for Portable Object. It is in the form of an editable text file having translation strings. You should use it for translations only.
3. .pot means Portable Object Template. It exists in the form of an editable text file. It is used to grasp the WordPress translation strings, themes and plugins.
Here is the process:
1. Duplicate and rename the .pot file as plugin-basename-lang_COUNTRY.po.
2. Use the reference plugin cased as subscribe-reloaded-fr_gr.po (fr_gr refer to French and German languages).
3. Mention your preferred language instead of French and German
4. Set WPLANG to your preferred language in wp-config.php file
5. PoEdit will automatically generate a .mo file every when you save the .po file. You need to upload this file for WordPress to use.
Hope this will help you!