As u/2nd_Can_Div stated, the continued recognition of German as a national language in Namibia is mostly a function of the sizable number of German immigrants that the area received during the colonial period. This level of German immigration didn’t really exist in Togoland, or any of Imperial Germany’s other possessions on the continent for that matter (i.e., Togoland, Kamerun, and German East Africa). But let me add a little more specificity to what transpired.

First of all, it’s important to note that, at present, German is only spoken at home, and in limited circles, by those White Namibians who are descended from the German immigrants who had come to what was then German South West Africa. During the 30 year period of German colonial rule, South West Africa received roughly 15,000 German immigrants, most of whom came to pursue diamond mining, agricultural opportunities, various forms of trade, and related colonial occupations, including a significant contingency of soldiers who were charged with protecting the interests of the settlers. The fact that German is still constitutionally recognized as a national language relates more to subsequent political developments than to the significance of its daily use in Namibian society. At present, no more than 30,000 Namibians, or less than 2% of the total population, speak German as their first language - and even that may be a generous estimate. For a variety of reasons, including emigration and other globalizing effects, the role of German in Namibia continues to be in decline.

German South West Africa existed from 1884 until 1915, when its colonial administrators eventually capitulated to the South African forces, which had invaded German South West Africa in September 1914 after the outbreak of hostilities in Europe. At the time, the Union of South Africa was a self-governing dominion of the British Empire. This began the period of South African occupation, which only ended in 1990. The South Africans were awarded a Class C Mandate by the newly formed League of Nations, which allowed them to administer the formerly German South West Africa according to South African law. Thereafter, and until Namibian independence in 1990, South Africa effectively treated Namibia as its fifth province. In doing so, certain privileges were extended to the landed German minority, including the recognition of the German language as a co-official, alongside Afrikaans and English. A lot of this has to do with the pro-German sympathies harbored by many Afrikaans-speaking South Africans, who formed the politically dominant white group within South Africa.

In 1990, the new Namibian constitution adopted English as the sole official language, largely in an effort to move away from the legacy of apartheid’s language policies, which favored Afrikaans and also afforded protection to the German minority's linguistic heritage. (Although this was also done to avoid the potential consequences of tribalism and to further support integration with the global economy.) However, in the spirit of reconciliation, which surrounded much of post-independence Namibian policy-making, the German language was recognized as a national language along with Afrikaans and the other Bantu and Khoisan languages that were spoken by many more of the country’s inhabitants.

In short, the demographic and political situation in Namibia exists in stark contrast to that of modern-day Togo, which never experienced the same level of German immigration and sustained influence. In fact, in 1913, Togoland was reported to only have a German population of 316 persons, the majority of whom would have been men that were posted there as part of the colonial administration (and likely left the country soon after World War I). German Togoland was eventually divided into French- and British-administered League of Nations mandates, the latter of which was consolidated with present-day Ghana, which retains English as its official language. Meanwhile, the French-administered portion of Togoland, which is what we refer to as Togo today, was administered by the French from 1916 until 1960 and was largely integrated into the shared colonial bureaucracy that served France's expansive colonial possessions in West Africa. This is why so much of West Africa retains French as an important regional lingua franca today.