conftest.py

import pytest
from selenium import webdriver
from selenium.webdriver.chrome.options import Options

def pytest_addoption(parser):
    parser.addoption('--browser_name', action='store', default="chrome", help='Choose browser: chrome or firefox')
    parser.addoption('--language', action='store', default='en', help='Choose language')

@pytest.fixture(scope="function")
def browser(request):
    browser_name = request.config.getoption("browser_name")
    user_language = request.config.getoption("language")

    if browser_name == 'chrome':
        options = Options()
        options.add_experimental_option('prefs', {'intl.accept_languages': user_language})
        print("\nStart CHROME browser for test..")
        browser = webdriver.Chrome(options=options)
    elif browser_name == 'firefox':
        fp = webdriver.FirefoxProfile()
        fp.set_preference("intl.accept_languages", user_language)
        print("\nStart FIREFOX browser for test..")
        browser = webdriver.Firefox(firefox_profile=fp)
    else:
        raise pytest.UsageError("--browser_name should be chrome or firefox")
    yield browser
    print("\nQuit browser..")
    browser.quit()