Choosing a language is an important task for a test automation engineer because projects may change, and programming languages (PLs) may change together with them. 

The project code and tests can be implemented in different programming languages, but it's better if these languages coincide. Firstly, it allows you to use a single infrastructure (development environment, libraries, plugins). Secondly, the processes of both development and automated testing on the project will be the same. And third, it will always be possible to use the knowledge of the developers to facilitate and accelerate testing. So, which language to choose?   

Java 

Java is one of the most popular languages. Therefore, the risk of "not matching the project language" with knowledge of Java is lower. Moreover, thanks to its cross-platform nature, this language is used to write applications for most modern platforms (except iOS). 

Java's advantages also include the fact that its ecosystem contains a large array of libraries and frameworks that, among other things, are related to automated testing: Cucumber—for describing test scenarios in readable form, JUnit—for unit testing, Selenium—for testing web graphic interfaces. 

The main disadvantages of this language are the performance of processes and the need for a large amount of disk space. But this difficulty is solved by a competent architecture of tests and test framework thanks to design patterns. 

It is considered a difficult language for beginners to master. But the main difficulty is in building the right algorithms and data structures, and this can be learned.   

С# 

C# is another suitable language to start a career in Automated Testing. Since 2016, thanks to the .NET Core platform, which is based on the “create once, run anywhere” concept, C# has been a cross-platform programming language, which allows it to be used on Windows, Linux, MacOS, Android, iOS and other systems. Using C# as the main programming language will enable you to write automated tests for any application easily. Selenium WebDriver and Playwright are great for UI, RestSharp for APIs, and Appium for mobile automation. If you need to create test scripts in a business-friendly C# language, you can use Gherkin syntax and SpecFlow as the main library to automate test scripts, thus following a behavioral approach in application testing.

Python 

Python is second to Java and C# in the number of software products (programs that solve customer problems) created in it. But its popularity has grown with the popularity of artificial intelligence, neural networks, and machine learning. Although the core of such technologies is usually written in C++, Python is widely used in these areas to create the "client layer" of software on which automated testing engineers most often work. 

The language is considered relatively easy to learn. Today, Python supports modern programming concepts and paradigms, particularly object-oriented programming. Another plus of Python is its rich ecosystem, which includes special libraries and frameworks for test automation.  

JavaScript 

It is considered to be a front-end language. That is why it is quite popular among the test automation community. JavaScript was originally a highly specialized language for writing browser scripts. However, it is now used to write server code. It can even be used to program embedded applications such as the Raspberry PI platform.  

JavaScript refers to a family of implementations of the standard ECMAScript. The most popular can be considered JavaScript and TypeScript from Microsoft. The main disadvantage of JavaScript is its strong fragmentation: a lot of redundant libraries don’t allow you to select a common set. 

Any of these programming languages is suitable for starting a career in Test Automation. Which one to choose depends on your personal preferences and the direction of the projects you want to develop in.