1. I beleive learning one language very well is best. Most people can then write and read other languages with some syntax differences.
2. An inital cert is good for getting an interview if you do not have several years of experience in that field/language already, the examples are good for showing proficiency and tha ability to deliver a working product which would be the later stages of an interview.
3. Python is one of the best languages for data analysis and would help in that field
4. Yes to back-end
5. Salesforce is not a language but rather a CRM, I would focus your time on Python.
If you have any other questions, let us know, happy to help.