Kovidgoyal, thank you for quick response. Currently I have not enough time to learn and write patch - but may be, later.
Now I shall use this workaround:
Category:Science
Tags:
Biologia
Biologia. Psychologia
Biologia. Psichologia. Love
...and so on. The items assign manually to all 3 tags.
Have a nice day!
P.S.
If somebody do this patch, please, be so kind, inform me about it!