String.Contains will only search for a single string: you will have to do multiple searches if you continue to use it.
You could use a Regex:
public static Regex regex = new Regex("hello|hola|salut", RegexOptions.IgnoreCase
| RegexOptions.CultureInvariant
| RegexOptions.IgnorePatternWhitespace
| RegexOptions.Compiled
);
MatchCollection ms = regex.Matches(InputText);