Though AIr WordPress default language is English, it is easy to translate into another language.
There are two main POT files ready:
/themes/air-theme2/languages/art-theme2.pot /plugins/bm-builder/languages/bm-builder.pot
You could translate the PO/MO file by Loco Translate WP plugin. Refer to the video tutorials on how to translate from the POT file.
There are the 6 translated(the strings in frontend pages) PO files including German, France, Spanish, Japanese, Chinese, Finnish. If your language is one of them. The PO files would be linked by default. You could edit the PO file. Please check the video tutorials(ps: the video is based on ART theme, but it is the same with Air theme):
There is a Loco Translate plugin official Doc here.
Tips: If it doesn’t work for some strings, please make the boxes empty in “Air Theme > Theme Options > General Settings: Descriptions”.