Some languages are very incomplete; warn about this

[ttencate]

Some languages are probably only complete to the extent that those birds occur in that region:

$ sqlite master.db
sqlite> select printf('%-5s', language_code), printf('%3d%%', count(*) / 10896.0 * 100.0) from common_names where common_name is not null group by language_code order by language_code;
af   |  9%
ca   | 93%
cs   | 90%
da   | 95%
de   | 98%
en   |100%
es   | 98%
et   | 52%
fi   | 93%
fr   | 99%
hu   | 60%
id   | 14%
is   |  8%
it   | 93%
ja   | 91%
lt   | 92%
lv   | 18%
nl   | 99%
no   | 97%
pl   | 99%
pt   | 53%
ru   | 88%
se   |  8%
sk   |100%
sl   | 10%
sv   | 99%
th   |  9%
uk   | 90%
zh_CN| 99%
zh_TW| 99%

For languages below, say, 80%, we should show something like "Thai (9% complete)" in the language selector menu.