Semantic similarity in text
Here's a simple technique.

Train an LDA using something like MALLET over your collection of texts. For each pair of documents you want to compare, obtain the topic distributions and compute the Hellinger distance between them.

Things you can tweak include term weighting, the LDA hyperparameters, and the metric for comparing distributions. Term weighting would obviate both the need for a list of important words, and the restriction to only English.