Internal redirect link script or alert

I have a large website (over 25000 pages) and they are primarily in English. We want to translate some of them into Spanish. However, as we are working, I noticed that we will have to link to English pages from Spanish pages.

I basically need a script that stores and screens the destination link address and if it contains a certain string of characters (in this case, the word "Spanish"), to take them through to the link destination or to a redirected page or alert letting the user know they are going outside of the Spanish-translated resources.

I am stuck using simple cross-browser coding and only scripts that will be accessible/508 since I write for a government website.