BOSTON — Vanguard's lineup of more than 170 mutual funds is diverse, but there's something lacking. The nation's largest mutual-fund company doesn't offer foreign bond funds, an area where low-cost options are hard to come by.

It has been a significant gap because there's been great investor interest recently in foreign bonds.

Investors deposited a net $31 billion into world bond funds for the 12-month period ended Sept. 30, according to Morningstar. That's more than any other fund category that Morningstar tracks. Emerging markets bond funds attracted $14 billion in new cash

All that's about to change. Vanguard announced plans this past week to introduce two such funds, one investing in government and corporate bonds around the globe, and another in bonds issued by governments in fast-growing emerging market nations. Vanguard filed applications with regulators, and expects to launch the funds in the first quarter of next year.