What is the best technology stack to choose for creating such an application?

Question

Mobile development

What are the options for the architecture (backend, frontend) of such an application (preferably, with an estimate of the price and term for different options)?
1. The application is a free cross-platform chat messenger (whatsapp type) with built-in automatic message translation to google translate api, its purpose is simple quick communication of people who speak different languages
​​2. The application must be uploaded to the Appstore and Google and available for download from them. After downloading the add-on, the user registers (enters his language, age, gender, city). If he writes to a person with a different language, he can automatically google translate (if he wants) or send in his own language
3. The received message may be incorrectly translated, but there should be an option to view the original message (or English translation)
4. Later, the app may have ads or the option to buy it for $1 without ads.
5. Budget - 130-950 thousand rubles

Answer 1

You, in fact, have a regular chat, on which the feature of automatic translation is "screwed".
For chat, you can take Parse.com - there is no need to write a backend, plus a bunch of features right out of the box.
Auto-translation - by calling the Google Translate API.
That's the whole technology stack.
PS The budget is delicious :))

Answer 2

On Sea Sharp using Xamarin it will be cheaper to develop applications for all the necessary platforms than to hire a specialist for each of them.