In the bad old days of isolation, shifters generally 'spoke' at least three languages: the language of their animal species, often more a matter of scent and movement than words, a human language, and the 'mother tongue'--a fully articulate '[shifter]-language' possible in any of the forms except, perhaps, the homid. This pretty much covered their communication needs.
These days, however, when a Garou's 'packmates' may very well include a Bastet, a Gurahl, or even a Mage or Kinfolk, something more is required. While communication with non-shifters remains difficult (although Kinfolk often learn how to understand, if not emulate, the animal and shifter languages of their kin), shifters have half-discovered, half-invented something of a mother-tongue pidgin which allows communication between species. Speaking in their shifter language, especially if taking some pains to be comprehensible, a Ratkin can be clearly understood by a Perunka, for example, although the accent will be considered highly bizarre, and there will inevitably be some words/concepts which do not translate.
The first few times a character speaks with a new species of shifter should be seen as a rich opportunity for roleplayed misunderstandings and frustrations, as the two speakers become accustomed to getting their ideas across.