How to make QGIS abbreviate labels with a dictionary?

I'm trying to use qgis "expression dialog" for labeling a layer. What I'm looking for is an expression that permits to apply some abbreviation rules on the layer. For now i'm using this

CASE 
WHEN nome2 is not null THEN  replace("nome1"  || '$' ||  "nome2",  'Wasserfall', 'Wssf.') 
WHEN nome2 is not null THEN  replace("nome1"  || '$' ||  "nome2",  'CascatA', 'Casc.')
WHEN nome2 is not null THEN  replace("nome1"  || '$' ||  "nome2",  'Cascate', 'Casc.e')
WHEN nome2 is null THEN    replace("nome1", 'Wasserfall', 'Wssf.')
WHEN nome2 is null THEN    replace("nome1", 'Cascata', 'Casc.')
WHEN nome2 is null THEN    replace("nome1", 'Cascate', 'Casc.e')
END

Obviously it doesn't work because only the first condition (wasserfall) is used for the label.

It happens something like that

Wasserfall$Cascata -> Wssf.$Cascata

instead of

Wasserfall$Cascata -> Wssf.$Casc.

I can solve the problem directly in postgis (with a view or a simple update) but if it is possibile to do it in qgis it would be great. Most of all it would be great to use an abbreviation dictionary but I'm quite sure that qgis (for now) is not able to doing it. I'm on W7 qgis 2.4.