This study designs and develops a multilingual specialized dictionary covering English, Vietnamese, and Lao, using a Binary Search Tree (BST) index for lookup on locally stored data. English terms are normalized into query keys linked to JSON-formatted definitions; when the tree is relatively balanced, lookup has 𝑂(log 𝑛) complexity. The system also supports approximate search based on string-matching scores. A dataset of 2,000 entries is used to examine the system. The comparisons show that BST reduces the number of comparisons and processing time relative to linear search in the average case, while this advantage diminishes when the tree degenerates