Question: At work we write a small to moderate amount of scripts to aid us in normal development. We have some people that are more comfortable in python, some in perl, some in php, etc...

Sometimes I think it is best to let people work in a language they are most comfortable with. This can mean that sometimes people can do a better job on a script (as they know more tricks in one language). It can also lead to less development time per script.

Other times I think that we would benefit the most from standardizing so that there might be more shared libraries and so that we don't get into the situation of "I can't work on that script because I don't know python".

Do you think that we should standardize or let people choose for each script they write?

Answer: 
I think the right place to ask this question is with your own team. 

Your team should form a consensus as to whether or not they want a common platform or whether they want the freedom to choose the right tool for the job. There is no single best answer to this question any more than there is a single best answer for "what's the best scripting language".

Certainly there are advantages to each approach. If every team member is free to choose their own language, they might be more productive and your business will reap the benefit. On the other hand, if someone writes a critical tool in a language only she knows and then something happens to her (illness, new job, etc) you can be stuck with a single point of failure that no one knows how to fix.
No. 

Your dev environment is hopefully a living entity that changes and is cultivated. New abilities (scripting languages) should be able to be accommodated, and older places that haven't been visited for years will someday get obviated by tools, or revisited from time to time and an evaluation will take place. Hopefully the dev scripts are a minor amount of development and automation. Chances are the team will drift towards a set of standards (ant, python, etc).