Since 16.04 russian name of the app Ubuntu Mate Welcome become "Добро пожаловат" instead of "Добро пожаловать". So it's one letter missing in the end. I checked the desktop file and it contains two strings with [ru], so the second one on the screenshot should be deleted an the first one is the correct "Добро пожаловать". Attaching screenshot:
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I have created a bug report on launchpad for this issue that you can see at https://bugs.launchpad.net/ubuntu-mate/+bug/1688560
I invite you to do the same for any future bugs you may find.
Happy MATEing 
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