Translation using PoEdit
The procedure is standard – you can find the .pot file in the plugin’s languages folder.
Please use PoEdit - https://poedit.net/ to translate the .pot file and create respective .po and .mo fies.
You should upload .po and .mo files created using PoEdit back to plugin's languages folder.
Please name .po and .mo files e.g. bt-cost-calculator-nl_NL.po and bt-cost-calculator-nl_NL.mo (nl_NL is the language code for dutch) and place them in /wp-content/plugins/bt_cost_calculator/languages/.
For other languages code, please refer to the following link: Internationalization.
You can set the site language of your WordPress installation on Settings > General. WordPress will automatically use the right language files if they exist.
Translation using Loco Translate
Install Loco Translate plugin - https://wordpress.org/plugins/loco-translate/ on Plugins panel of your wp-admin console
Once you have the plugin installed and activated, please do the following:
1. Go to Loco Translate > Plugins.
2. Click on Cost Calculator.
3. Click on Advanced tab and set Text Domain and File Prefix to “bt-cost-calculator”. By default they are probably “bt_cost_calculator”.
4. Set Template file to languages/bt-cost-calculator.pot and Save Config. Go to Overview Tab.
5. Click New Language and choose the language you have set in WordPress > General Settings.
6. Set Choose location to Author (plugins/bt_cost_calculator/languages/bt_cost_calculator-xx_XX.po).
7. Click Start translating.
8. Translate the strings you need - you do not have to translate the entire set.
9. Once you save the translation, the changes should be visible on Front End if you have done everything as described.