These menu items should each have an ellipsis. I was hesitant to try these menu items. Without an ellipsis to denote more input required, their labels present as if the command will execute immediately and can not be cancelled.
Tools Menu > Join Files
to: Tools Menu > Join Files...
Tools Menu > Split File
to: Tools Menu > Split File...
The manual changes have all been done for the next update. (For the help file that ships with the program. The web version will also be fixed but updates on a different schedule.)
The "Join Files" and "Split File" labels have been updated internally, but may be left as-is until a larger set of string changes happen, due to the extra noise and delays minor changes can cause our translation process. (Once changed, they'll also only affect new installs, unless the existing toolbar is reset to factory defaults. But if you want the change on your existing toolbar now, you can edit in the changes, of course.)