After long thinkings I want to try rewrite my game in Pascal.

And I have few questions:

• what disadvantages has that compiler, in comparison with the IS-BASIC (or ZZZIPed BASIC);
• what Pascal function/procedure can use instead Basic's DATA statement;
• howto using channels: write/writeln to specified channel (because EP scecific functions has description only on magyar);

Zzziped version has problem.
One sunny day zzzip compiler said me: "Too many labels".
And I can't finish game in full size.

One sunny day zzzip compiler said me: "Too many labels".

If the program is too long you can take out some parts, create a loader and put the parts taken out into the loader. E.g. envelope number, set character can go to the loader.
You can try to contract some lines into one line, e.g.:
10 SET STATUS OFF
20 SET KEY CLICK OFF
30 SET BORDER 0
They can be conctracted and you can get a single line instead of three ones:
10 SET STATUS OFF:SET KEY CLICK OFF:SET BORDER 0
(These are only examples.)
If you use more DATA lines, you can contract them too.

You can try to use shorter variable numbers (I don't really know if it counts.)
If you use variables that are needed only in certain parts of the program (so you don't need them any more), you can use the same variable name for this function. So you can reduce the total number of variables used.
These are my suggestions.