You can translate theme text strings (for example the weekdays) on two different ways:

1. Translate theme language file

You can translate the theme by editing the included .pot language file with a program like PoEdit. After translating please export the .po and .mo files which you need to upload in the language folder of the theme (theme-folder/language/). 

For more information please see this link

2. Translate with the Loco Translate plugin

With the Loco Translate plugin you can translate the theme inside your WordPress installation.

Please install and activate the Loco Translate plugin and follow the steps below:

1. Navigate to Loco Translate -> Themes (to translate text from a plugin go to Loco Translate -> Plugins)
2. Click on the theme or plugin in the list that you want to translate.
3. Click on the "New Language" link
4. Set your language from the dropdown field
5. Set "Choose a location" to Custom and press the Start Translating button
5. Type the word you want to translate in the search box and click on it when it appear in the list below
6. Write your translation in the most bottom textarea (do not change the default text)
7. Save the settings
8. Navigate to Settings -> General and set the "Site Language" option to the translation language.

You can read this tutorial for more information how to set-up a new translation (screenshots included)