Hmm... I think there is something missing in the file you used from Arne.
Here are the keys for Library Tab and the monitor tabs. Also I attached you the current Lang.properties file I have, if other keys are missing too.
# Library Tab
Library = Library
TTTLibrary = Overview of the shared library.
LibraryMnemonic = L
LibraryAccelerator = control 5
SharedFiles = Shared Files
Rescan = Rescan
# SearchMonitorTab
SearchMonitorTab_SearchMonitor = Search Monitor
SearchMonitorTab_TTTSearchMonitor = Monitor searches going through your node.
SearchMonitorTab_Mnemonic = m
SearchMonitorTab_Accelerator = control 8
SearchMonitorTab_enable = enable
SearchMonitorTab_Show = Show
SearchMonitorTab_Rows = rows.
# ResultMonitorTab
ResultMonitorTab_ResultMonitor = Result Monitor
ResultMonitorTab_TTTResultMonitor = Monitor search results going through your node.
ResultMonitorTab_Mnemonic = R
ResultMonitorTab_Accelerator = control 9
ResultMonitorTab_ResultFilter = Result Filter
ResultMonitorTab_TTTPassiveSearch = Specify keywords to match, separated by space.
ResultMonitorTab_StartPassiveSearch = Start Passive Search
ResultMonitorTab_TTTStartPassiveSearch = Passive search monitors the search results routed through here. This might take a while.
ResultMonitorTab_StopPassiveSearch = Stop Passive Search
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