The World Intellectual Property Organization in Geneva makes available a Patent Cooperation Treaty Glossary.
WIPO recommends it as “a useful tool for Offices and applicants in understanding the PCT and drafting or translating PCT documentation”. The glossary is available in French, Russian, Spanish, Portuguese, German, and English – you change languages using the roll-down menu at top right of the website.
Each term has direct links to selected relevant references in the various languages to articles, sections and rules.
The glossary can be found here.