Question:

I have a database query based on user input, However if the user inputs any one common letter in the search the app will crash. but as the search also supports Chinese characters I can't simple block all one character searches.

How would I write a regular expression to check for a single English character but will not include a single Chinese characters? "^(a-zA-Z){1}$" "^\w{1}$" do these include only english letters??

I'm thinking of using the regular expression like this, but any better solutions would be appreciated:

if(input.matches("^(a-zA-Z){1}$") { //Show error } else { //do query }

You should definitely fix any crashes first. To distinguish between English and Chinese (CJK) characters, you can use character classes such as \p{ASCII}, \p{Alpha} for ASCII and \p{InCJKUnifiedIdeographs} for CJK characters.