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

Question

I am using Retrofit2 + OkHttp3 in my Android application to make a GET request to a REST Server. The problem is that the server does not specify the JSON encoding that it passes. This causes the "é" to be accepted as the "" (Unicode replacement character).

Is there any way to tell Retrofit or OkHttp that encode the response?

This is how I initialize Retrofit (Kotlin code):

val gson = GsonBuilder()
        .setDateFormat("d.M.yyyy")
        .create()

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

val retrofit = Retrofit.Builder()
        .baseUrl(RestService.BASE_URL)
        .client(client)
        .addConverterFactory(GsonConverterFactory.create(gson))
        .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
        .build()

val rest = retrofit.create(RestService::class.java)

PS: The server is not mine. Therefore, I cannot fix the original problem on the server side.

Edit: final decision

class EncodingInterceptor : Interceptor {

    override fun intercept(chain: Interceptor.Chain): Response {
        val response = chain.proceed(chain.request())
        val mediaType = MediaType.parse("application/json; charset=iso-8859-1")
        val modifiedBody = ResponseBody.create(mediaType, response.body().bytes())
        val modifiedResponse = response.newBuilder()
                .body(modifiedBody)
                .build()

        return modifiedResponse
    }
}

Answer 1

- Interceptor, Content-Type :

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
    }
}

OkHttp :

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

OkHttpClient API, , , .

Answer 2

class FixEncodingInterceptor implements Interceptor {

    @Override
    public Response intercept(Chain chain) throws IOException {
        Response response = chain.proceed(chain.request());
        MediaType oldMediaType = MediaType.parse(response.header("Content-Type"));
        // update only charset in mediatype
        MediaType newMediaType = MediaType.parse(oldMediaType.type()+"/"+oldMediaType.subtype()+"; charset=windows-1250");
        // update body
        ResponseBody newResponseBody = ResponseBody.create(newMediaType, response.body().bytes());

        return response.newBuilder()
                .removeHeader("Content-Type")
                .addHeader("Content-Type", newMediaType.toString())
                .body(newResponseBody)
                .build();
    }
}

OkHttp:

builder.addInterceptor(new FixEncodingInterceptor());