How to specify Get-Request encoding (Retrofit + OkHttp)

One way to do this is to build an Interceptor that takes the response and sets an appropriate Content-Type like so:

class ResponseInterceptor : Interceptor {
    override fun intercept(chain: Interceptor.Chain): Response {
        val response = chain.proceed(chain.request())
        val modified = response.newBuilder()
                .addHeader("Content-Type", "application/json; charset=utf-8")
                .build()

        return modified
    }
}

You would add it to your OkHttp client like so:

val client = OkHttpClient.Builder()
        .addInterceptor(ResponseInterceptor())
        .build()

You should make sure you either only use this OkHttpClient for your API that has no encoding specified, or have the interceptor only add the header for the appropriate endpoints to avoid overwriting valid content type headers from other endpoints.