https://en.wikipedia.org/wiki/Executive_Order_8802
Note that in Hawaii, Japanese-Americans were a significant portion of the local population, about one-third. Of the 150k+ Japanese-Americans living in Hawaii, only 1,200 to 1,800, or about 1%, were interned. On the mainland US where they were a smaller portion of the population, far more Japanese Americans were interned. This discrepancy probably comes down to a matter of practicality again; one third of the population is just too many to intern.
Anti-German sentiment was certainly present in America and the UK during the world wars. In response to Anti-German sentiment, the British royal family anglicized their name during WWI, changing it from House of Saxe-Coburg and Gotha to House of Windsor. In America, German Americans largely stopped speaking German in public (German was the second most common language in America and was spoken particularly often in Pennsylvania, remnants of which can still be seen today in "Pennsylvanian Dutch" culture.) However, treating German Americans as severely as Japanese Americans were treated, at least on the mainland, was probably too impractical to be considered.
https://en.wikipedia.org/wiki/German_Americans#The_apparent_...
It could also be argued that it made sense to do the same for Germans since we had a minority of Germans siding with Hitler and even holding Nazi rallies before we got involved in WWII. We weren't exactly good arbiters of fairness when it came to race either.