Thank You for your quick reaction
Now when I change my site into english, there aren't polish tags but english tags are shown only when they are in first position in "tags" table in database - see screenshot
table "tags"
I check table "categories" in my database & see that polish & english names are in the same line
table "categories"
When I change language (when I'm showing "Archives") the adequate name of category is shown.
The tags are in other lines.
Maybe there is bug in pixelpost engine?