French localization: translation of the 4 empty strings (#1433)
French localization: translation of the 4 empty strings (#1433)

* French localization: translation of the 2 empty strings
* French localization: translation of the 2 other empty strings

bartsch-dev/jabref,JabRef/jabref,mairdl/jabref,Mr-DLib/jabref,oscargus/jabref,tschechlovdev/jabref,jhshinn/jabref,shitikanth/jabref,bartsch-dev/jabref,mredaelli/jabref,JabRef/jabref,obraliar/jabref,zellerdev/jabref,obraliar/jabref,tschechlovdev/jabref,ayanai1/jabref,sauliusg/jabref,sauliusg/jabref,mairdl/jabref,jhshinn/jabref,shitikanth/jabref,jhshinn/jabref,tobiasdiez/jabref,motokito/jabref,oscargus/jabref,motokito/jabref,Mr-DLib/jabref,bartsch-dev/jabref,motokito/jabref,mairdl/jabref,ayanai1/jabref,oscargus/jabref,shitikanth/jabref,grimes2/jabref,grimes2/jabref,Mr-DLib/jabref,grimes2/jabref,Braunch/jabref,tobiasdiez/jabref,Mr-DLib/jabref,tobiasdiez/jabref,tobiasdiez/jabref,mredaelli/jabref,Siedlerchr/jabref,jhshinn/jabref,motokito/jabref,Siedlerchr/jabref,sauliusg/jabref,mredaelli/jabref,grimes2/jabref,JabRef/jabref,ayanai1/jabref,zellerdev/jabref,zellerdev/jabref,Braunch/jabref,zellerdev/jabref,tschechlovdev/jabref,mairdl/jabref,oscargus/jabref,Braunch/jabref,JabRef/jabref,ayanai1/jabref,tschechlovdev/jabref,Siedlerchr/jabref,shitikanth/jabref,obraliar/jabref,shitikanth/jabref,bartsch-dev/jabref,bartsch-dev/jabref,sauliusg/jabref,motokito/jabref,Braunch/jabref,ayanai1/jabref,Braunch/jabref,mredaelli/jabref,obraliar/jabref,Siedlerchr/jabref,jhshinn/jabref,zellerdev/jabref,oscargus/jabref,mredaelli/jabref,grimes2/jabref,mairdl/jabref,obraliar/jabref,tschechlovdev/jabref,Mr-DLib/jabref