WHERE
(TO_TSVECTOR('german', description -> 'de') @@
PLAINTO_TSQUERY('german', 'foobar')
)::int +
(TO_TSVECTOR('french', description -> 'fr') @@
PLAINTO_TSQUERY('french', 'foobar')
)::int +
(TO_TSVECTOR('english', description -> 'en') @@
PLAINTO_TSQUERY('english', 'foobar')
)::int
> '0'
A cast of a boolean to integer is 0 or 1. When comparing an integer to a text the text will be cast to integer.