“两党连立”（通常指两党联合执政或两党联合组阁）常见的英文表达可以是 "a coalition government between the two parties" 或 "a two-party coalition" 。
"a coalition government between the two parties" 明确指出是两党之间组成的联合政府。
"a two-party coalition" 简洁地表达了两党联合的意思，可根据具体语境判断是否需要补充“政府”（government）等词汇。
例如：
They formed a coalition government between the two parties to stabilize the political situation.（他们组成了两党联合政府以稳定政治局势。）
The election resulted in a two-party coalition.（选举后形成了两党联合的局面 。 ）