I think this is a really interesting issue. Whilst this situation doesn't apply to me in therapy, my partner's first language is not English although they are fluent. It definitely makes a difference to how we connect emotionally. I think we lose some nuance and certainly a lot of commonly understood emphases. Sometimes it is hard work and I feel a distance between us. Consequently, I struggle more than usual to express myself when I am distressed. I can imagine that this would be intensified in a therapeutic relationship. Do you think your therapist experiences "something missing" as well?