A first general answer is: Usually not. Your language certificate is part of your application and must, therefore, be handed in before the application deadline.
However, some universities grant applicants the option to apply with a placeholder, for example, a language certificate on a lower level, and hand in the actually required language certificate later. The applicant can be admitted under the condition that they will provide a language certificate at a high enough level when they enroll.
Keep in mind that if you have to apply for a visa, you will also have to hand in a proof of language proficiency or of your intention to take a language course to show that you are an eligible and serious candidate and can obtain the visa. Time management is therefore crucial.