Finally, after some googling I found the answer posted here:
I have examined it a little further. It appears that the commandtext is
saved in the resource when it's length is more the 200 characters. This not
only applies to the commandtext property, but to all string properties, e.g.
the Label.Text. It's saved to the resouce even if the localizable property of
the form, usercontrol or component is false. When you decrease the length of
the string, the property is removed from the resource file and placed in the
Designer.cs file.
So it seems you have no control over the fact if a lengthy string is saved
in the resource or not. In the case of the commandtext that's very
dangerouse, because a translator of the resource could change the commandtext
to a wrong statement.
Apparently there's not way to change this behavior. I did confirm there is a 200 character limit excluding white space.