[__app_dev__]

Based on your skills I would highly recommend Python and some JavaScript.

Python being the main language to focus on because it's great for working with data and general scripting needs (working with files, etc). For data everything from basic data access to a lot of math and statistics that you would find in R.

I would recommend some JavaScript so that you have the ability to easily read it and because I feel that when you learn multiple languages it improved your skills overall for each language. Doesn't have to be long - perhaps a few days of focused learning (or even a day or less).

Recently I have been working on something related to using a lot statistics, analytics, etc and have been using Python the most for it and actually some SQL as all major databases now support Percent Rank and other statistical functions. For my project I'm using JavaScript a little for work such as Web Scraping but most work is done in Python and then final reporting is SQL.

Python is also great for Machine Learning. Even for basic API access with TensorFlow I prefer using Python over there JavaScript API.

Good luck with your new career!