In 1999 I started programming applications and websites. Since then I met several languages at various levels.
Counting only languages for use on computers, I'd say I know from html to C, through JavaScript, VBA, ASP, SQL, AutoLISP, * .NET and a lot of things along the way. Certainly I know some languages more than others, and will lose the practice of not used languages, but in general, I can remember each one, after some contact time.
Speaking of development environments, languages and technologies, I started with Delphi, then HTML, followed by Javascript and ASP. Currently, unless there is some requirement, I use Lazarus to computer programs, PHP for internet, and, for embedded devices, I use C or assembly.
Each item will have its specified license, that preferably will be the BSD 2-Clause License, but some may have other licenses.
The BSD 2-Clause License have only one requirement to allow the use of the licensed object: to reproduce the copyright notice and the license text in its entirety on the source of the final object code when it is distributed, and in a way that it can be accessed by the user when the final object is compiled code. In the second case (compiled), the license reproduction can be on documentation, but must not be possible to distribute the object without such documentation.
Obviously the user is solely responsible for the use, results and consequences.