The plugin has two localization files. One for an admin and one for a frontend page. In most cases you need to localize only a frontend page. Localization files are inside the language folder of the plugin.
If you just want to change a button title, you can make it in the plugin setting: Content Egg -> Settings -> Buy now button text / Coupon button text
To make a localization from the admin page with the most comfort way, we recommend to use the plugin Loco translate. You need to make some setup before using the plugin to edit frontend files. Go to Loco translate – Plugins and find Content Egg. Then, go to Setup tab and make next settings. (This can be set automatically. If so, then don't change anything here).
Save the file. Now you can create a new language or use an existed language for a frontend localization.
To create a new language, click on link “New language”
The plugin uses own setting for a language and doesn't use a language setting of wordpress. Set a language in Content Egg –> General Settings –> Language of your site.
Choose Custom language and set locale (two letters) which you have in the Content Egg –> General Settings –> Language of your site.
When you create a new language in Loco translate, it must be without a second part. For example, for Finish, a file name must be “fi”, not “fi_FI” as usual in wordpress.