Translation:This bus is slow, you know.
How would you say 'this bus is LATE'. I can imagine contexts where either could make sense but they really mean something quite different. A bus can be fast in terms of speed, but late (maybe they spent too long picking up passengers or the driver started their shift late), and vice versa
The English translation of your second example is grammatically incorrect.
Fixed version: "Sorry for coming/being late." or "I'm sorry [that] I am late." (In English, "to be late" implies the action of coming from somewhere else, so it doesn't need to be explicitly stated with that verb.)
I think "This bus is so slow" makes more sense than adding the "you know" at the end - the latter makes it Uncanny Valley English (It checks out grammatically, but no one says 'you know' for something like this).
よ is an emphasis particle, so the word "so" when describing something (or "really") would be a better fit.
I think in some instances either is a valid translation for osoi, because if you think about it if the bus is slow then it either is or it's going to be late. Also yo is more like an exclamation mark. And in Japan buses and trains are ALWAYS on time (unless there's been an accident) so a slow bus would definitely be late! ; )
That doesn't mean that a bus is slow though - it would be driving (one would hope) at the same legal speed as everyone else - it might mean that it takeslonger to get to the same destination than a bus that had a more direct route but it doesn't mean that the bus itself is slow. It would just mean it had a lengthier route.
If we're talking about an intra-city bus, I would normally think "This bus is slow" refers primarily to the fact that because of all the stops it has to make / traffic / whatever else its overall progress is slow. This does not at all imply that it is somehow running behind the scheduled timetable.
Could be a dialect difference.
Is the "you know" よ not simply the equivalent of ending an obvious statement with something like "eh?", or other rhetorical request for confirmation?
Or is it an attempt to mark something as fact, wherein rather than rhetorically requesting confirmation, you're actually implying, "I fully expect you to agree with me."
In other words, is this more like:
This bus is slow, eh?
This bus is slow, clearly.
Hmmm, i thought the よ at the end of a sentence was like a superlative mainly used by men (like for emphasis) and mainly women would ね at the end of the sentence rhetorically (like 'isn't it'). I got this understanding from a native speaker. So based on that i would have thought this sentence meant "this bus is really slow". Could someone clarify the usage of this?
The よ at the end of this sentence can also mean "for sure" like if you just realized that the bus you are going with is slow and you say to your friends "this bus is for sure slow" this can also bring the idea is very slow just adding a "ちょっと" to the sentence and it can mean "unacceptable slow".