The string is so long that there is no margin between label and window left border.
One solution could be to move the input fields X_MARGIN to make this fit but this change would affect area for customization image.
Another solution is to change the layout from:
Label [ input field ]
[ input field ]
This change would also remove the "need" for check translation lengths due to excessive amount of horizontal space for label.
Fixed by making the client window wider. The screenshot in the TAG is also updated.
Verified that the tlclient login window fits the russian translation, but also that every other supported language still fits.
The documentation looks good as well.