midgey- why not? Some people choose a religion not because they are 'born with it' but because they find it attactive and true to them.
My mothertongue is French, but I always spoke English when I lived in UK, unless family or friends came to visit. Now we live back where my roots, are, DH has made huge effort to learn FRench, which has earned the respect of all- but we speak English together, sometimes when we are out, in shops, or restaurants, if we are out as a couple. Of course we speak French if in company. We watch UK TV most of the time too.
WE both speak both languages every day, jumping constantly from one to t'other depending on context or whom we speak to- both have books on the go in both languages- for us it's totally 'normal'.
We have friends here who speak 2 separate languages to their children, eg dad always speaks Danish, for example, and mum always speaks Italian, if together they speak English as the common family language, and the kids speak French at school, and then learn German from aged 10.