Because of the generally more favorable corporate tax rates abroad, international stocks can, on occasion, offer enormous yields that are sustainable in the long term. The international investing landscape, though, can also present unique challenges that make it difficult to identify the best income opportunities.

Armed with this insight, we asked three of our Foolish investors which high-yield international stocks they think might be worth buying right now. They recommended AstraZeneca plc (NASDAQ:AZN), Mobile TeleSystems (NYSE:MBT), and Brookfield Infrastructure Partners (NYSE:BIP). Read on the find out more. 

Picture of a hand stacking euro coins.

Image source: Getty Images.

Are better days ahead?

George Budwell (AstraZeneca): Despite the late-stage failure earlier this year of its lung cancer immunotherapy of Imfinzi plus tremelimumab, which was supposed to return the company to sustainable growth, shares of the British pharma giant AstraZeneca have still acquitted themselves admirably in 2017. Thanks in large part to its healthy annualized dividend yield of 8.35%, Astra's stock has so far produced a remarkable total return on capital of 28% at the time of writing. 

Apart from its monstrous yield, there are also a couple of sound fundamental reasons for Astra's outstanding, market-beating performance in 2017. First off, Astra's broader oncology pipeline has been progressing without a hitch for the most part over the past few years. As a result, the drugmaker now sports two major new cancer medicines besides Imfinzi -- namely Tagrisso for mutated epidermal growth factor receptor cancers and Lynparza for advanced ovarian cancer.

Astra also recently filed for the approval of its next-generation BTK inhibitor, acalabrutinib, for patients with previously treated mantle cell lymphoma. This potential blockbuster medicine could be approved as early as January 2018 and quickly become a key growth driver for the pharma titan in the years ahead.

At the end of the day, though, Astra's 91.8% trailing payout ratio and fairly weak balance sheet remain serious concerns for dividend and growth investors alike. The company is likely to pursue additional acquisition targets in the near term in case Imfinzi fails to redeem itself in advanced lung cancer after all. Such a move would clearly put the drugmaker's sky-high yield at risk, and perhaps require the company to take on even more debt. 

From Russia with dividends 

Sean Williams (Mobile TeleSystems): If you're looking for a high-yield international stock, and are willing to take on above-average risk (which means you also have a shot at above-average share-price appreciation), my suggestion would be to dig into Russia's Mobile TeleSystems.

Mobile TeleSystems, one of the largest wireless-plan operators in Russia, has come on hard times in recent years. Growth rates have slowed a bit as there have been concerns about wireless-subscription saturation. Mobile TeleSystems has also come under fire during a U.S. corruption probe that saw it sell its stake in an Uzbekistan joint venture. Usually, investors would be wise to keep their distance from corruption probes and slower growth rates, but I view these setbacks as merely a bump in the road for this dominant wireless giant.

Arguably the biggest growth catalyst for Mobile TeleSystems is the expansion of wireless transmission capacity in Russia and its adjacent countries. In the U.S., 4G or LTE speeds are available almost everywhere. This isn't the case in Russia, where faster speeds are still being upgraded in many medium- and small-sized cities. Consumers have shown that they're willing to upgrade their smartphones and/or their data plans in order to have access to faster data, which puts Mobile TeleSystems on the cusp of what could be a second major growth cycle. What's even better is that the growth in data plans tends to be high-margin, meaning even single-digit growth in sales can lead to a much-larger increase in profit.

Investors shouldn't overlook the company's market share, either, which gives Mobile TeleSystems pricing power where it operates. As of mid-2015, the company boasted nearly a third of wireless-plan market share in Russia, Turkmenistan, and Ukraine, as well as close to 60% share in Armenia. Its size makes it a go-to for consumers, and makes it a popular partner for smartphone manufacturers.

A one-of-a-kind company

Brian Feroldi (Brookfield Infrastructure Partners): Income investors should favor companies that provide an essential service, have a competitive moat, crank out predictable profits, and share the wealth with investors. One company that checks all of these boxes perfectly is Brookfield Infrastructure Partners.

While Brookfield calls Canada home, the company owns and operates a motley group of infrastructure assets spread around the world. This includes assets like electricity transmission lines in Chile, communication equipment in France, timberlands in North America, toll roads in South America, shipping terminals in Australia, and more.

What all of these one-of-a-kind assets have in common is they face little competition (or none at all) and throw off predictable amounts of cash flow in good times and in bad. Management's policy is to reinvest a portion of the profits back into growing its asset base and pay out the remainder to shareholders. 

This bulletproof formula has worked like a charm. Investors have earned market-smashing returns since this company's 2008 IPO.

BIP Total Return Price Chart

BIP Total Return Price data by YCharts.

Looking ahead, management believes that its dividend will grow between 5% and 9% annually. And considering the company's dividend yield of 4%, Brookfield Infrastruture Partners is a great international stock for income investors to get to know.

This wireless giant is not without its fair share of geopolitical risks, but it's also paying out around 7% with its semi-annual dividend and sports a reasonably low forward P/E under 10. That seems like a good risk-reward balance to this investor.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.