Here's what the IRS's Pub 970 says about qualified educational expenses:
For purposes of the lifetime learning credit, qualified education expenses are tuition and certain related expenses required for enrollment in a course at an eligible educational institution. The course must be either part of a postsecondary degree program or taken by the student to acquire or improve job skills.
That's a little clearer (and, in my opinion, broader) than the article. Foreign languages can be used on the job. Trade skills, if they are taught at an eligible educational institution, are definitely a job skill. It seems that those are clear "yes" answers. The certification in "a discipline" is a likely yes, as well.
I say a likely yes because, I was hoping for further guidance from the US' Internal Revenue Code. 26 USC §25A(f)(1) states:
The term “qualified tuition and related expenses” means tuition and fees required for the enrollment or attendance of the taxpayer [and a few others] at an eligible educational institution for courses of instruction of such individual at such institution.
which seems even broader. However, 26 USC §25A(f)(2) states:
Exception for education involving sports, etc.
Such term does not include expenses with respect to any course or other education involving sports, games, or hobbies, unless such course or other education is part of the individual’s degree program.
I think that exception is where the slight vagueness in both your article and the IRS' guidance comes from--it's not literally any college class offered by a qualified educational institution, it's the academic ones, defined broadly. As such, if you're getting a certificate in something that's not sports-related, based on the guidance of the IRS and the Internal Revenue Code, it seems that those would also qualify.