'Although' paired with 'yet' in a sentence?

It's archaic, which means that acceptability is declining.

Although he was bad with calligraphy, yet he tried his best to write a letter to her on her birthday.

The yet in that sentence reinforces the trying. A more-or-less equivalent form — but less archaic are more generally acceptable — might be

Although he was bad with calligraphy, still he tried his best to write a letter to her on her birthday.

Because it's essentially there for emphasis, the yet [or still] should be stressed when reading the sentence.

It does not sound right. The sentence works better without the yet OR without the although

Also I would not use bad in this case

Although his calligraphy was poor, he tried his best to write a letter to her on her birthday.

Or

His calligraphy was poor, yet he tried his best to write a letter to her on her birthday.'

I believe it is a Chinese misunderstanding judging from the posts I find on google

The yet could be an older version of still. I would object less if the yet came after he, making it sound slightly Shakespearean:

Though his calligraphy was poor, he yet/still tried his best to write a letter to her on her birthday.'

It's rare in modern-day English, but I've been reading some John Locke and he uses the concessive "although-yet" clause frequently.