Translation:This is my girlfriend; she likes to sleep.
I agree...we call this a "comma splice" in English, and it's very incorrect; although people do it all the time. Drives me nuts as often I see it in presumably "professional" publications. These two ideas would either be two separate sentences or at the very least be separated by a semicolon.
There's no harm in just using a second comma there. That would be the correct punctuation; it wouldn't be a comma splice. If you wanted to avoid using two commas in that sentence, the way to do it would be to replace the first comma with a semicolon, and drop the word 'and'. But you need a comma before 'although' either way.
Semicolons aren't just replacements for commas; they require independent clauses (basically, complete sentences) on either side. They really are closer in usage to periods than they are to commas.
I suppose you are correct; I was trying to avoid a run-on sentence as I'd already used one comma. I often use semicolons to connect closely-related ideas while avoiding comma splices, as my sentences tend to be long. It's actually become my favorite form of punctuation.
I guess it's just the way we talk and write. It seems natural in Russian to unite short sentences that describe the same thing or share object or subject. It's not incorrect to use period or conjunctions in these cases, but sometimes it just looks and sounds weird. Maybe it's simply something one should get used to while learning Russian.
P.S.: English punctuation still confuses the hell out of me every once and a while.
I realize that the comma separating two independent clauses is correct in Russian, but it is not correct in English. There should be an option to keep the comma in English and construct a subordinate clause such as "who likes to sleep." While not a direct translation, it connects the sentences in a similar way.
I think "This is my girlfriend; She likes sleeping" would be a better translation. The Russian text suggests that the girl likes sleeping in general; Therefore the gerund (-ing) is more appropriate. "...She likes to sleep" could be interpreted that she would like to sleep a.s.a.p.
'She likes sleeping' and 'She likes to sleep' mean 100% the same thing in English. 'She likes to sleep' cannot be interpreted as she would like to sleep ASAP as you say.
Perhaps you are thinking of 'She would like to sleep' - which is a more formal way of saying 'She wants to sleep'.