Google Paly Store ASO is not only about making literal translations, give sense to what you translate and make it friendly for users reading the app description.
Title 50 characters, Short Description 80 Characters
You have the tools to make a good research. The main purpose of finding good & relevant keywords is to make the client's app more "easy to find" (optimize it)
Try to think like a regular person searching for something. For example, How would you search a running app? - the best tool is your brain.
The main reason of app owners to care so much about their keywords is simply because from all the searches people do, the 60% becomes an install.They care for appearing in the top places of results displayed, so they'll have more chances to acquire a new user.