For bioinformatics, which language should I learn best and common after graduation?
Please refer to the following threads and use the search function as this has been discussed extensively before:
Best Language For Bioinformatics
What is the most popular programming language used in bioinformatics?
Programming languages for Bioinformatics
Which Are The Best Programming Languages For A Bioinformatician?
I personally learned R first as the Bioconductor repository harbors many essential packages for my work related to NGS analysis, such as tximport, DESeq2, csaw etc. Still, python is also a good choice. Look around in the web for tutorials and choose the language you feel more comfortable with. Both are recommended for bioinformatics.
For biological background graduates, Python and R should be the best languages to learn.
If you only want one language, then go with Python first.
As recommended by fellow biostar membres, I will go with R and Python. Look at this article i wrote sometimes back