There's a difference between the message resources from htmlconv1_3_1.jar and
the message resources in the l10n workspace on sekai.eng.

For example, Converter.java may be different so LCs will need new resources
and need to update the resources for localization ASAP.

htmlconv1_3_1.jar in htmlconv_pit has:

Usage: java -jar htmlconv1_3_1.jar [-option1 value1 [-option2 value2 [...]]] [-simulate] [filespecs]

------------------------------------------------------------------------
Options:

-source: Path to get original files. Default: <userdir>
-dest: Path to write converted files. Default: <userdir>
-backup: Path to write backup files. Default 'dirname <directory_of_html_file>'/'basename <directory_of_html_file>'_BAK
-subdirs: Should files in subdirectories be processed.
-template: Path to template file. Use default if unsure.
-log: Path to write log. If not provided, no log is written.
-progress: Display progress while converting. Default: true
-simulate: Display the specifics to the conversion without converting.

Filespecs: Space delimited list of file specs, * wildcard. (*.html *.htm)

Converter.java in jdk1.3.1_l10n has:

Usage: java -jar htmlconv-13.jar [-option1 value1 [-option2 value2 [...]]] [-simulate] [filespecs]

------------------------------------------------------------------------
Options:

-source: Path to files. Default: <userdir>
-backup: Path to write backup files. Default 'dirname <directory_of_html_file>'/'basename <directory_of_html_file>'_BAK
-subdirs: Should files in subdirectories be processed.
-template: Path to template file. Use default if unsure.
-log: Path to write log. If not provided, no log is written.
-progress: Display progress while converting. Default: true
-simulate: Display the specifics to the conversion without converting.

Filespecs: Space delimited list of file specs, * wildcard. (*.html *.htm)

As far as I know, the "-gui" option should be there also.