Check file storefront/language/french/french.xml
See if you can find
<definition>
<key>text_sorting_price_asc</key>
<value><![CDATA[Price Low > High]]></value>
</definition>
If you do have have this entry, you will need to add it.
NOTE: You will need to delete language entries from database for french section and clear cache before you will see the result reloaded.