How can I run tesseract with multiple languages one time?

Try this:

custom_config = r'-l eng+jpn --psm 6'
txt = pytesseract.image_to_string(img, config=custom_config)

from langdetect import detect_langs
detect_langs(txt)

Note: you have to install langdetect by using:

 pip install langdetect

Since tesseract 3.02 it is possible to specify multiple languages for the -l parameter.

-l lang The language to use. If none is specified, English is assumed. Multiple languages may be specified, separated by plus characters. Tesseract uses 3-character ISO 639-2 language codes.

An example:

tesseract myscan.png out -l deu+eng