Final answer:
Informal language would be most appropriate for a dinner at a neighbor's birthday party.
Step-by-step explanation:
The most appropriate language style for the given situation, which is a dinner at a neighbor's birthday party, would be informal language. Informal language is more casual and relaxed, which would be suitable for a social gathering with friends and neighbors. It allows for a friendly and comfortable atmosphere, allowing everyone to engage in conversations without feeling too formal or restricted.