The author, in this paper, analyzes the significance of the interpreter’s language competence and the need for language knowledge acquisition in professional interpreting. As China is in great need of qualified interpreters, interpreters must possess an extraordinary array of qualifications in order to achieve interpreting competence. Among these, language competence is a prerequisite requirement for any interpreter to start the profession. And to strive for interpreting competence, interpreters must enhance the language competence and consolidate their language knowledge throughout the career. Acquisition of language knowledge, therefore, remains an essential skill of interpreters.This paper is divided into five chapters, excluding an introduction and a conclusion.In the introduction, the author explains the purpose of this paper. The author pointed out that language knowledge, as an essential and important component in the knowledge base, seldom gets its due emphasis. As interpreters are generally generalists, it is interpreters’ language competence that distinguishes them from other bilinguals and provides them a solid base to fulfill various tasks in even highly specialized fields. Therefore, language competence and the acquisition of it deserve full attention.In Chapter One, the author defines the components of interpreting competence by proposing the Xiada Model for Interpreter Training. It is argued that language competence is essential nevertheless most important for the interpreting efficiency. As extralinguistic knowledge is rather volatile and dynamic in the knowledge base, interpreter’s acquisition of language knowledge is an essential skill to enhance the interpreting competence and to improve their language knowledge.Chapter Two elaborates on the basic requirements of an interpreter’s language knowledge. Interpreter, as a communicator of message in the bilingual communicative activity, should have a good command of the working languages in order to ensure a successful act of communication. Interpreter’s language requirements are therefore discussed in details at the level of phonology, syntactics, semantics, pragmatics and terminology, which are useful aspects of language knowledge in interpreting. Interpreters’ interpreting competence is firmly built upon the language competence.While the previous chapter talks about the language competence required of an interpreter, Chapter Three examines the language competence in the process of interpreting. Throughout the whole process, language command plays an essential role in ensuring the interpreter’s performance. Interpreter’s whole body of language knowledge is activated from listening comprehension to reformulation. Language competence of the interpreter will definitely reduce the efforts required and contribute to the solution of interpreting problems.Chapter Four moves on to two major language issues in interpreting: linguistic availability and language specificity. The author wants to point out that many interpreting students’ poor performances result not from lack of enough Words and Rules, but from lack of enough available Words and Rules. As interpreting requires highly available Words and Rules, strategies are implied from Gile’s GravitationalModel. Furthermore, as interpreting is a language-based activity involving many interlingual differences, language specificity training offers very practical implications for C-E interpretation.Chapter Five is devoted to the discussion of language knowledge acquisition andlanguage proficiency enhancement in professional interpreting. Knowledgeacquisition is an essential skill, and it leads up to the interpreter’s long-term languageknowledge build-up. Strategies for language knowledge acquisition are put forwardwith the focus on the language part, especially on terminologies. The last part of thechapter deals with the language proficiency enhancement of interpreters. It followsthat interpreters should work toward the goal of language proficiency throu