Interlac

"As the official U.P. language, Interlac is taught in schools throughout the system and is the common form of communication between most sentient United Planet races."  - Who's Who in the Legion of Super-Heroes #   1

Interlac is a DC Comics fictional language. It is the main language used by 30th century United Planets (think the United Nations IN SPACE) in the Legion of Super Heroes comics. It was first referenced in Adventure Comics # 379.  However, the actual letters and numbers weren't reveal until years in Legion of Super-Heroes (Volume 2) # 312 by writer Paul Levitz and artist Keith Giffen. 
Language / Numbering System
The language has 26 letters that corresponds with each the English letters and it's numbering system uses a ten as a base (as shown above). As such, it has ten digits corresponding with 1, 2, 3, 4, 5, 6, 7, 8, 9 and 0. However, the numbering system is flawed due to 42 and 7 looking the same. It has a similar problem with 41 and 6. Despite being written differently, Interlac sounds exactly like English.
Babylon 5
In Babylon 5, there is an unrelated language also called Interlac. This version of Interlac is a universal language based on math. This is flawed idea to the possibility of aliens having non-decimal based numbering system.
Reference:
http://en.wikipedia.org/wiki/Interlac