"I am constantly amazed at how many claim to jump on the caring for immigrant ideology - yet discriminate at will against foreign born priests, claiming they don't adapt to the language..."

First, how far do you reckon Jesus would have got with His ministry if he was not fluent in Greek and Aramaic?
Second, a lot of immigrants start off in jobs that don't require the fluency in English required of a priest, who is after all required to explain sometimes complex theological and pastoral issues. Many immigrants are glad to have a job, and what's more don't mind being in jobs below their competence level if it means their children have a chance to make it good in their adoptive country.
Third, many priests from overseas are not always happy to be out of their cultural milieu - they feel like a fish out of water. An unhappy priest is not an effective priest.