What does “I can just about stand learning something” mean?

I came across the phrase, “I can just about stand learning the filthy lingo it’s written in,” in the following sentence in the article titled “The Dragon’s Egg – High fantasy for young adults” appearing in The New Yorker magazine’s December 5 issue.

“Incoherent and often inaudible” was Kingsley Amis’s verdict on his teacher (Oxford Professor, John Ronald Reuel Tolkien). Tolkien, he reported, would write long lists of words on the blackboard, obscuring them with his body as he droned on, then would absent-mindedly erase them without turning around. “I can just about stand learning the filthy lingo it’s written in,” Philip Larkin, another Tolkien student, complained about the old man’s lectures on “Beowulf.”

I don’t understand what “I can just about stand learning the filthy lingo it’s written in,” mean.

Is “can (be able to) about stand + gerund” a popular idiom or set phrase?

It means the writer can barely tolerate learning the filthy lingo it's written in.

To stand something means to endure it/to be able to get through it (usually with some difficulty). In this case he's not talking about difficulty in understanding but that he finds it distasteful (the "filthy lingo" = dirty/rude vocabulary) - the addition of "just about" simply emphasises the difficulty.

"I can't stand + gerund" and "I can stand + gerund" are common phrases but I wouldn't call them idioms.

"Can't stand losing you" is a popular song by The Police.