Why can Toll-like receptors be found either inside and outside the cell?
TLRs are used to identify features that are typical of pathogens. Different TLRs tend to identify different features, so that a wide range of pathogens can be identified. Some of these pathogens may be extracellular (such as some kinds of bacteria that are recognized by TLR4, which is extracellular) and some are intracellular, like viruses (some of which may be identified by TLR7, which is intracellular).  

The fact that innate immune cells have these is a little bit of a red herring, because they aren't limited to innate immune cells -- they're widespread among many cell types, and are effective at protecting the specific cell, not just activating innate immune cells.