We suggest you to try using this plugin: Loco Translate. It can be used for changing theme’s static text strings and plugins as well.
Step 1: Install the plugin from your WP Dashboard => Plugins => Add New
Step 2: Go to Loco Translate -> Themes to select your theme
Step 3: Add new language, choose the language you want to add for translations. To change the default static text strings you can simply click “Edit Template”
Step 4: Search for the text you want to translate or change from the default language file and enter your changed/translated word in place.
If the translation doesn’t work or some words cannot be found, make sure that you are using the latest version of theme and the website has only one copy of the theme installed and then press the ‘Sync’ button in the Loco Translation page.