Ability for critical systems to perform optimally is a major concern for both the customer demanding for such system and the software engineer. This paper takes a critical look at the term "critical system", the types, and its sensitivity. Hence, if a critical system does not perform as expected it will impact seriously on life, environment and valuable assets. To ensuring an optimal performance of a critical system, there is underlying software that enhances its performance. The most emergent property of a critical system is dependability which is a function of the software used in designing the system. Dependability in a system implies that the system consist of the following functions; availability, reliability, safety and security. This paper focuses on the programming language support for dependability and performance for critical system. To what level does each of the language discussed in this paper support dependability of critical system and how possible is it to achieve dependability as well as performance. Finally, this paper also proposes a language rating for dependability of critical system. This will enable software engineers to evaluate this rating to make a proper choice when developing software for critical systems.