WING Lung Bank, a 28-branch medium-sized bank, has announced a 21 per cent increase in profit for last year, to $472.8 million from $391.1 million. Final dividend was $1.32 a share. A bonus issue of one share for every five shares held was declared. Coupled with the interim dividend of 40 cents, the total payout for the year would be $1.72, only a 2.38 per cent increase over the previous year. ''The business of the bank remained steady last year,'' the company said. Total deposits and other accounts grew 20.1 per cent to $26.3 billion. Total assets increased 19.9 per cent to $28 billion. The bank is developing automated services to meet the needs of customers. ''Under the persistent economic development in China and the Asia-Pacific region, the bank holds an optimistic view about the economy of Hong Kong in 1994,'' the bank said.