Examples of using "неестественно" in a sentence and their english translations:
- This is not natural.
- It's unnatural.
It doesn't sound natural.
It's very easy to sound natural in your own native language, and very easy to sound unnatural in your non-native language.
Generally, the sense whether or not an expression is natural can't really be relied on. For example, even if it feels unnatural, it is often easily due to lack of experience.
That may be, but making a mistake is not equivalent to saying something unnatural. If someone confuses "your" and "you're", it doesn't call into question their being a native speaker.