"They are too tired."

Translation: 他们太累了。

[Drinc]

What was the lesson where 太...了 has been explained in the web version?

[George792719]

These two Chinese girls on Youtube are very good at explaining all the different uses of 了.

www.youtube.com/watch?v=JjAGEjr6-kY

[FlviaGiese]

I can't remember, but you might try this site: https://resources.allsetlearning.com/chinese/grammar/Expressing_%22excessively%22_with_%22tai%22
or this one: https://www.chineseboost.com/grammar/le-grammar-summary/

[George792719]

I've also noticed since a female voice has replaced the male Chinese speaker, sometimes she says 'Le' and other times what sounds like 'Lao'.

[PonyFreckles]

When the character is being said in isolation? Liǎo is another pronunciation of the 了 character, just not in the contexts we've learned it so far. When there's no context the automated voice has to 'choose' between alternate pronunciations and doesn't always get it right.

[Jason137255]

Basically 了 in this context is being used as the "intensifier particle." Think of it like how 吗 acts like a question mark 了 acts like an exclamation point.

[Semeltin]

I have heard that this means too exhausted.