I think & sign is for shorcuts with Alt-letter to work, but i think it shouldnt be visible on buttons etc. Probably this is some bug or mistake in translation files.
Yes, you should convert your translation file to unicode after you do changes. Netbeans does it for me when i need to change something.
I have attached the latest french translation file, though you can extract it anytime from Spark.jar. spark_i18n_fr.properties.zip (8443 Bytes)