Adding international bonds to an individual investor's portfolio is a controversial subject. On top of the standard risks of bonds you are adding country specific risk, currency risk and diversifying your individual company risk. In theory many of these risks should be rewarded but the data are noisy at best and adding risk like developed currency risk may not be rewarded at all.
Also, most of the risk and diversification mentioned above are already added by international stocks. Depending on your home country adding international or emerging market stock etfs only add a few extra bps of fees while international bond etfs can add 30-100bps of fees over their domestic versions. This is a fairly high bar for adding this type of diversification. US bonds for foreign investors are a possible exception to the high fees though the government's bonds yield little.
If your home currency (or currency union) does not have a deep bond market and/or bonds make up most of your portfolio it is probably worth diversifying a chunk of your bond exposure internationally. Otherwise, you can get most of the diversification much more cheaply by just using international stocks.